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rRC:SP:77-2008 MANUAL FOR DESIGN CONSTRUCTION & MAINTENANCE OF GRAVEL ROADS INDIAN ROADS CONGRESS 2008 i

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Page 1: MANUAL DESIGN CONSTRUCTION MAINTENANCE …IRC:SP:77-2008 CONTENTS PersonneloftheHighwaysSpecifications&StandardsCommittee Abbreviations vi 1. Introduction 1.1.PersonnelofRuralRoadsCommittee

rRC:SP:77-2008

MANUAL FOR DESIGNCONSTRUCTION & MAINTENANCE

OF GRAVEL ROADS

INDIAN ROADS CONGRESS2008

i

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Page 4: MANUAL DESIGN CONSTRUCTION MAINTENANCE …IRC:SP:77-2008 CONTENTS PersonneloftheHighwaysSpecifications&StandardsCommittee Abbreviations vi 1. Introduction 1.1.PersonnelofRuralRoadsCommittee

Digitized by tine Internet Arcliive

in 2014

Iittps://arcliive.org/details/govlawircy2008sp77

Page 5: MANUAL DESIGN CONSTRUCTION MAINTENANCE …IRC:SP:77-2008 CONTENTS PersonneloftheHighwaysSpecifications&StandardsCommittee Abbreviations vi 1. Introduction 1.1.PersonnelofRuralRoadsCommittee

IRC:SP:77-2008

MANUAL FOR DESIGN,CONSTRUCTION & MAINTENANCE OF

GRAVEL ROADS

Published by

INDIAN ROADS CONGRESSKama Koti Marg,

Sector 6, R.K. Puram,

New Delhi-no 022

2008

Price Rs. 400.00

(Packing & Postage Extra)

Page 6: MANUAL DESIGN CONSTRUCTION MAINTENANCE …IRC:SP:77-2008 CONTENTS PersonneloftheHighwaysSpecifications&StandardsCommittee Abbreviations vi 1. Introduction 1.1.PersonnelofRuralRoadsCommittee

IRC :SP:77-2008

First Published : September, 2008

(All Rights Reserved. No Part of this Publication shall be

reproduced, translated or transmitted in any form or by any

means without the permission of the Indian Roads Congress)

Printed at: I G Printers, Okhla Phase-I, New Delhi- 110 020

(500 Copies)

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IRC:SP:77-2008

CONTENTSPersonnel of the Highways Specifications & Standards Committee

Abbreviations vi

1. Introduction

1.1. Personnel of Rural Roads Committee 1

1 .2. Global Acceptance For Low Volume Traffic 2

1 .3. Life Cycle and Amenability to Stage Development 4

1.4. Techno-Socio-Economic Aspects 4

1.5. Influence of Environmental Conditions on Performance 5

1.6. The Problems of Local Moorums, Maintenance & Dust Control 6

1.7. Warrants for Sealing 7

1.8. Potential for Large Scale Applications and Employment Generation 7

1.9 Demonstration Projects 8

2. Design of Gravel Roads

2.1. Geometric Design Standards 8

2.2. Materials 9

2.3. Pavement Design for Gravel Roads 16

2.4 Drainage Design 25

2.5. Rehabilitation of Gravel Roads 33

3. Construction and Quality Control

3.1. Choice of Technology 35

3.2. Plant Selection and Usage 41

3.3. Sequence of Construction Operations 41

3.4. Earthwork and Subgrade Preparation 41

3.5. Sub-base Construction 43

3.6. Gravel Base/Surface Course Construction and Quality Control 48

3.7. Providing Gravel Surface 52

3.8. Sealing a Gravel Road 53

3.9. One-Coat and Two-Coat Surface Dressing 53

3.10. Step-wise Procedure for One-Coat and Two-Coat Surface Dressing 54

3.11. Step-wise Procedure for Providing 20 mm Bituminous Premix Carpet 55

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IRC:SP:77-2008

4. Maintenance Methods and Management System

4.1. General 56

4.2. Surface & Structural Defects on Gravel Roads 57

4.3. Maintenance of Gravel Roads 60

4.4. Maintenance of Shoulders, Drainage and Structures 72

4.5. Special Problems of Hill Road Maintenance 74

4.6. Maintenance Management 75

4.7. Organizational Aspects of Maintenance Management 77

4.8. Do's and Don'ts 78

Appendix 2.1 79

Bibliography 84

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IRC:SP:77-2008

PERSONNEL

1. (Convenor)

2. Singh, Nirmaljit

(Co-Convenor)

3. Sharma, Arim Kumar(Member-Secretary)

4. SinhaV.K.

5. Ahluwalia, H.S.

6. Bahadur, A.P.

7. Basu, S.B.

8. Chandrasekhar, B.P., Dr.

9. Datta,P.K.

10. Desai, J.P.

11. Deshpande, D.B.

12. Dhingra, S.L., Dr.

13. Gupta, D.P.

14. Gupta, K.K.

15. Jain, N.S.

16. Jain, R.K.

17. Jain, S.S., Dr.

18. Kadiyali, L.R., Dr.

19. Kandaswamy, C.

20. Krishna, Prabhat

OF THE HIGHWAYS SPECIFICATIONS ANDSTANDARDS COMMITTEE

(As on 7* November., 2007)

Add!. Director General Ministry of Shipping, RoadTransport & Highways, New Delhi

Member (Tech.), National Highways Authority of India,

New Delhi

Chief Engineer (R) S&R, Ministry of Shipping,

Road Transport & Highways, New Delhi

Secretary General, Indian Road Congress

Members

Chief Engineer, Ministry of Shipping, Road Transport

& Highways, New Delhi

Chief Engineer, Ministry of Shipping, Road Transport

& Highways, New Delhi

Chief Engineer (Pig.), Ministry of Shipping, RoadTransport & Highways, New Delhi

Director (Tech.), National Rural Roads Development

Agency (Ministry of Rural Development), New Delhi

Executive Director, Consulting Engg. Services (I) Pvt.

Ltd., New Delhi

Sr. Vice-President (Tech. Sen), Gujarat Ambuja CementLtd., Ahmedabad

Vice-President, Maharashtra State Road Development

Corporation, Mumbai

Professor, Indian Institute of Technology, Mumbai

DG(RD) (Retd.), MOSRT&H, New Delhi

Chief Engineer (Retd.),Haryana

Chief Engineer, Ministry of Shipping, Road Transport

& Highways, New Delhi

Chief Engineer (Retd.) Haryana PWD, Sonepat

Professor & Coordinator, Centre of Transportation

Engg., IIT Roorkee

Chief Executive, L.R. Kadiyali & Associates, New Delhi

Member (Tech.), National Highways Authority of India,

New Delhi

Chief Engineer (Retd.), Ministry of Shipping, RoadTransport & Highways, New Delhi

i

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IRC:SP:77-2008

21. Kukreti, B.P.

22. Kumar, Anil

23. Kumar, Kamlesh

24. Liansanga

25. Mina, H.L.•

26. Momin, S.S

27. Nanda,P.K.Dr.

28. Rathore, S.S.

29. Reddy, T.S., Dr.

30. Sachdev, V.K.

31. Sastry, G.V.N.

32. Sharma, S.C.

33. Sharma, V.M., Dr.

34. Shukla, R.S.

35. Sinha,A.V.

36. Srivastava, H.K.

37. Velayudhan, T.R

1 . President, Indian Roads Congress

2. Director General (Road Dev.)

3. Secretary General

1. Borge,V.B.

2. Justo, C.E.G., Dr.

3. Khattar, M.D.

Chief General Manager, National Highways Authority

of India, New Delhi

Chief Engineer (Retd.), CDO, Road Constn. Deptt.,

Ranchi

Chief Engineer, Ministry of Shipping, Road Transport

& Highways, New Delhi

Engineer-in-Chief& Secretary, Mizoram PWD, Aizawl

E-in-C/Secretary to the Govt, of Rajasthan, PWD, Jaipur

Former Member-Maharashtra Service Commission, Mumbai

Director, CentralRoadResearch Institute, NewDelhi

Secretary to the Govt, of Gujarat, Gandhinagar

Senior Vice-President, NMSEZ Development

Corporation Pvt. Ltd. Mumbai

Chief Engineer, MOSRT&H

Engineer-in-Chief (R&B), Andhra Pradesh PWD,Secunderabad

DG(RD) & AS (Retd.), MORT&H, New Delhi

Consultant, AIMIL, New Delhi

Ex-Scientist, Central Road Research Institute, New Delhi

Chief General Manager, National Highway Authority of

India, New Delhi

Director (Projects), National Rural Roads Development

Agency, (Min. of Rural Dev.), New Delhi

Addl. DGBR, Directorate General Border Roads,

New Delhi

Ex-Officio Members

(Patel, Subhash)

(Prakash, Indu) Ministry of Shipping, Road Transport&Highways, New Delhi

(Sinha, V.K.), Indian Roads Congress

Corresponding Members

(Past-President, IRC), Secretary (Roads), Maharashtra

PWD, Mumbai

Emeritus Fellow, Bangalore University, Bangalore.

Executive Director, Hindustan Construction Co. Ltd.,

Mumbai

4. Merani, N.V Principal Secretary (Retd.), Maharashtra PWD, Mumbai

(ii)

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IRC:SP:77-2008

ABBREVIATIONS

AADT : Annual Average Daily Traffic

AASHTO : American Association of State Highway and Transportation Officials

ALD : Average Least Dimension

CBR : California Bearing Ratio

cm : Centimetre

CVPD : Commercial Vehicles Per Day

ESAL : Equivalent Standard Axle Load (18 kips i.e. 80 kN)

GWT : Ground Water Table

HCV : Heavy Commercial Vehicle

HFL : High Flood Level

IS : Indian Standard

km : Kilometre

m : Metre

MCV : Medium-Heavy Commercial Vehicle

MDD : Maximum Dry Density

MORD : Ministry of Rural Development

mm : Millimetre

OMC : Optimum Moisture Content

PCI : Pavement Condition Index

PI : Plasticity Index

PMC : Pre-Mix Carpet

SD : Surface Dressing

TRRL : Transportation and Road Research Laboratory ofUK

VDF : Vehicle Damage Factor

WBM : Water Bound Macadam

(iii)

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IRC:SP:77-2008

MANUAL FOR DESIGN, CONSTRUCTION& MAINTENANCE OF GRAVEL ROADS

1. INTRODUCTION

1.1. The Rural Roads Committee (H-5) of the Indian Roads Congress approved theth

document in its meeting held on 9 June 2007 subject to incorporation of comments of the

members by the Sub-Group constituted for the purpose. The draft document was then finalised

by the Sub-group comprising S/Shri S.C. Sharma, RK. Katare,Dr. N.B. Lai and Shri Gurdip S.

Khinda. The personnel ofRural Roads Committee (H-5) as on 9*^ June, 2007 are as follows:

Gupta, D.R ... Convenor

Chandrasekhar, B.R Dr. ...Co-Convenor

Katare, RK. ...Member-Secretary

MembersAgarwala, S.K. Kumar, Praveen, Dr.

Baliga, Sushant Mina, H.L.

Datta, RK. Nanda, RK., Dr.

Dev, RN. Prakash, H.S.

Kadiyali, L.R., Dr. Sarkar, A.K.

Kalra, B.B. Sharma, S.C.

Kand C.V., Dr. Sharma, S.K.

Krishna, Prabhat Singh, Amrit Inder

Kumar, Ashok, Dr. Engineer-in-Chief, A.RKumar, Anil Director, HRS

Corresponding MembersJusto, C.E.G., Dr. Mitra, G.C., Prof

Singh, C.K., Dr.

Ex-Officio MembersPatel, Subhash President, IRCDG (RD), MOSRT&HSinha, V.K. Secretary General, IRC

The draft Manual finalised by the Sub-group as well as by Convenor, H-5 Committee

was placed before the Highways Specifications & Standards Committee (HSS) in its

meeting held on 7* November, 2007. The HSS Committee approved the draft with some

modifications. The modified draft document was put up before the IRC Council in its

meeting held on 16* November, 2007 at Jaipur during 68*'' Annual Session of IRC and the

Council approved the draft document for publishing as IRC document.

1

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IRC:SP:77-2008

1.2. Global Acceptance for Low Volume Traffic

1.2.1. Internationally, the unpaved roads (i.e. roads without bituminous or cement

concrete surfacing) constitute a sizable proportion of the total road length. In several

countries, the unpaved road length is more than the paved road length, as can be seen in

Fig. 1.1. In India, however, the unpaved road length constitutes less than half the total road

length (Fig. 1.2.). While in most countries abroad, among the unpaved roads, it is the Gravel

Roads, which are most popular, the unpaved roads in India are generally WBMsurfaced. More recently, especially with the World Bank assistance in some rural areas of In d i a

,

Gravel Roads showing good performance even after about 5 years of service have begun to earn

the confidence ofrural road engineers in the country.

UNPAVED ROAD LENGTH

17 18 PAVED ROAD LENGTH

BRAZIL SOUTH CHINA MEXICO CANADA AUSTRALIA INDIA

AFRICA

Fig. 1.1 The Unpaved to Paved Road Length Ratio in Selected Countries

(Source : CIA World Fact Book 2005)

1.2.2. As per AASHTO 'For the aggregate surfaced (Gravel) roads (used for manycounty and forest roads), the maximum traffic level considered is 100,000 ESALapplications' and "The practical minimum traffic level that can be considered for any

flexible or rigid pavement during a given performance period is about 50,000

applications". Assuming that commercial vehicles constitute about 25% of the number of

vehicles plying per day (and that the heavy commercial vehicles/trucks

constitute 20% of all commercial vehicles per day). Gravel Roads are suitable for anADT upto

200 vehicles day. Further, it implies that unless the daily traffic is of the order of about 125

vehicles per day, paved road (flexible or rigid pavement) is not justified. A recent study shows

that for traffic upto 200 vehicles per day Gravel Roads have lower maintenance costs compared

to black topped roads.

2

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IRC:SP:77-2008

Hofto Kong, China ^99S

Armenia 2000

Thafland 1999

Singapore 1999

KazakhsUn2000

Srt Unka 1999

Ceofgla 2000

Azertaijan 2000

Uzbekistan 1S99

Tajtkstan 1989

Turkmeflisian 1

Bhutan 1999

Japan 1999

Korea, Rep of 1993

Malaysia 1999

lussian FederaSon tSdsASSB

Pakistan 1809

ean«)lade»h 1999j U

trunei Otnnsalam I999f

New Zealand 3000

ineSa 1999

Imn, islamic Rep 199^

Fii 1999

Indonesia 1999

Nepal 1999

Samoa 199l(

PmireSla 1999

Turkey 1999

Tonga 1999

Viet Naml99?ji

Vanuatu 1999

China 1999

Philippines 2000

Cambodia SCXXt

Afghaf^slan 1999

Myanmaf 1S99

Mongo^a 2000

Korea POR 1

PNG 1999

SoK»mofl isianite 19'

100%

Sources: United Nalions and ESCAP Statistical Yearbooks, which have used datafrom Gauntry Statistical

Yearbooks. For the Russian Federation these sources were supplemented by the Europa Yearbook and World

Highways, September 1998 andfor Mia by the India Statistical Abstract 1999.

Fig 1.2 : Proportion of Paved Road in Selected Economies of tlie ESCAP Region

3

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IRC:SP:77-2008

1.2.3. There are several access roads providing connectivity to smaller habitations with

a traffic volume that is likely to be much lower than 200 vehicles per day. In such situations, the

most suitable and economical option that emerges is the provision of an aggregate surfaced

(gravel) road. It may be appreciated that after the current programme ofproviding all-weather

access to habitations with a population over 500 has been completed, substantial inputs will still

be required to provide all-weather access to the smaller habitations with a population less than

500, where the traffic generated would generally be of a much lower order justifying provision

ofGravel Roads as a first stage option from both technical and economic considerations.

1.3. Life Cycle andAmenability to Stage Development

1.3.1. It is also estabhshed that well-engineered Gravel Roads perform satisfactorily for low

volume traffic conditions provided theneededroutine andperiodic maintenance are attended to promptly.

For most situations, the maintenance requirements are frequent but inexpensive.As in the case ofblack -

topped roads, where bituminous surface renewals are required after about every 5 to 6 years or so

dependingon traflSc, the GravelRoads too require re-gravelling periodically. Ifthe periodic re-gravelling

requirement is attended to adesign lifeof 10 years canbe considered forpurposes ofpavementdesign. For

many low-volume traflSc conditions e.g., on Unk roads connecting habitations of relatively lower

population levels. Gravel Roads can continue to serve for long periods of time. If, however, the traffic

volume and axle loads increase to a levelbeyondthe traffic load carrying capacityofa Gravel Roadand its

serviceability level comes down close to the terminal serviceabihty level, strengthening / rehabilitation

withan overlaycanbe easilyimplementedtobring it topavedroad standards.

1.3.2. Thus, one ofthe biggest advantages of initially adopting a Gravel Road option for

low volume traffic conditions is its amenability to providing a thin bituminous surface treatment

or strengthening the pavement crust followed by black topping as may be warranted by

increased traffic. If a Gravel Road needs to be black topped as warranted by increased traffic

and environmental conditions, the bituminous surface treatment can be provided over the gravel

base after suitably preparing the surface of the existing gravel base and priming it as per

specified procedure. Where warranted by increased traffic considerations, structural

strengthening by way ofan overlay ofgravel /WBM/WMM etc. layer can be provided, treating

the existing gravel base as a lower base course or a sub base.

1 .4. Techno-Socio-Economic Aspects

1.4.1. The technical aspects of adopting a Gravel Road option for low volume rural

roads include the maximized use of the low cost locally available materials and deployment of

low-cost low-capacity equipment/plant both for construction and maintenance. Thus the

requirements of materials, plant and equipment for construction and maintenance can be

accomplished within the available resources and skills in rural areas. Since no bituminous

surface treatment is envisaged at least during the initial few years of its service life, there is no

requirement of expensive bituminous materials or the hot mix plants and equipment for manu-

facture, laying and compaction ofthe bituminous mix.

1.4.2. Studies carried out under the aegis of IRC in nine selected districts on socio-

economic impact ofrural roads show that a number ofsocial benefits (like access to education and

4

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IRC:SP:77-2008

health faciHty etc.) and economic benefits (improved transportation of agricultural produce,

higher yield / acre, quick transportation of perishable crops etc.) accrue from the provision of

rural roads. Social and economic benefits accrued from all-weather unpaved gravel roads are

practically the same as for black topped roads.

1,5. Influence ofEnvironmental Conditions on Performance

Gravel Roads for low volume traffic conditions in rural areas work out to be the most

suitable and economical option only under certain environmental conditions. These are:-

1.5.1. Availability of quality gravel within economic leads: Where the locally

available gravels meet the specified requirements of grading and plasticity for use in the

gravel base and surfacing as such, without any further processing, and are available

within short leads, say less than 5 to 10 km, Gravel Roads would generally work out to be the

most preferred alternative. However, where further processing by way of blending

with other local materials or by lime/cement treatment is required, the related costs

should be worked out and compared with the cost of other low-cost alternatives like paving with

bricks, stones, cement concrete blocks, as feasible. Similarly when the

distance of haulage of gravel is too long, the cost of haulage must be considered and compared

with the cost ofother alternatives.

0

1.5.2. Rainfall: High intensity ofrainfall causes high gravel loss on a gravel road as also

when the total annual rainfall is high, i.e. over 1500-2000 mm per year. However, it is more

meaningful to consider the combined effect of traffic and rainfall on the rate of

deterioration of a gravel road surface. Although no systematic performance records of gravel

roads for different amounts of rainfall are available, it is observed that under high

amount of rainfall, over 1500 mm/ year, a Gravel Road can take upto 100 vehicles per day; for

medium rainfall of 1000-1500 mm per year, a Gravel Road can take upto 150 vehicles per day

while for low rainfall less than 1 000 mm, a Gravel Road can take upto 200 vehicles per day.

1.5.3. Prolonged dry seasons: In areas with prolonged dry seasons, say 8 months or

more ofdry periods during a year, the gravel surface loses, under traffic or by wind, the very fine-

sized particles which provide the binding at the surface. As a result, dust nuisance is caused all

around the unsealed road. In such situations, it becomes necessary to use dust palliatives. If,

however, the cumulative cost ofproviding dust palliatives works out to be higher than the cost of

sealing the surface, a low cost thin bituminous surface treatment can be resorted to.

1.5.4. Longitudinal gradients: In the low rainfall regions, with less than 1000 mm/year,

the longitudinal gradients should not be steeper than 6%. Where the rainfall is in the range of

1 000 to 1 500 mm/year, the longitudinal gradients should not be steeper than 5%, provided proper

precautions are taken to prevent erosion.

1.5.5. Traffic volume: When the traffic volume is upto 100 vehicles per day, (excluding

2-wheelers), Gravel Roads are considered suitable except in case ofvery poor subgrade. Where

the traffic volume is upto 150 vehicles per day (excluding two-wheelers). Gravel Roads are

considered suitable except for the weak subgrades upto CBR of 4. For traffic upto 200 vehicles

per day (excluding 2-wheers), Gravel Roads are suitable for subgrades with CBR of5 and above.

For traffic volume above 200 vehicles per day (excluding two-wheelers). Gravel Roads are not

5

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IRC:SP:77-2008

considered suitable.

1.6. The Problems ofLocal Moorums, Maintenance& Dust Control

1.6.1. Local moorums: In India, the term 'Moorum' is commonly used to define soils and

gravels ofcertain types. Contrary to this belief, there is no soil group termed as 'Moorum' in the

Indian Soil Classification System or any such classification system internationally.

1.6.1.1. It is, therefore, not only desirable but necessary that moorum samples fi"om any

source and at various depths from that source must first be classified as per the Soil

Classification system before considering them for use in a Gravel Road. It may be pointed out

here that many 'moorums' do not even classify as 'Gravels' by the IS Soil Classification System; in

fact, several varieties when tested for their particle size distribution and their Liquid and Plastic

Limits, get classified as 'Clayey Sands' (SC).

1.6.1.2. As per the Indian Soil Classification system, any soil sample that has more than

half its weight retained on IS:75 micron sieve is a coarse-grained soil. Ifany coarse-grained soil

has more than half the weight of its coarse fraction retained on IS sieve of 4.75 mm size, it is a

'Gravel', denoted by the symbol "G". All Gravels are further classified as under, by the Indian

Soil Classification System:

• Well-graded Gravels GW Uniformity Coefficient>4

(Percent Fines>5%)

• Poorly-graded Gravels GP Not Satisfying GW requirements

(Percent Fines<5%)

• Silty Gravels GM(Percent Fines> 12%)

• Clayey Gravels GC(Percent Fines>12%)

As per the specified requirements, only the gravels classified as GW and GP may be suitable for

use in Gravel Base Courses whileGM an GC types are not suitable. For use in Gravel Surfacings,

GM and GC may ormay not be suitable whileGW and GP are generally unsuitable.

1.6.1.3. In view of the above, it is absolutely necessary for any Gravel Road project,

before incorporating local moorums that representative samples from each source and at

different depths be tested for their particle size distribution through standard set ofsieves and for

their liquid limit and plastic limit values. From the classification test data thus obtained, it would

be possible to classify them by the Indian Standard Soil Classification System. It is only

depending on the classification/soil groups to which the local moorums belong, that it would be

possible to decide whether these can be used as such or only after further processing in lubbase,

base or surfacing. Where further processing is required, the related costs should be worked out in

detail. Comparing the cost of local moorums after processing, with the cost of other alternative

low-cost materials like bricks, stone blocks etc, a decision may be arrived at in favour ofthe most

suitable and economical alternative

.

Below A-line of Plasticity Chart or

PK4

Above A-line of Plasticity Chart and

PI>7

6

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IRC:SP:77-2008

1.6.2. Maintenance and dust control

1.6.2.1. The performance of Gravel Roads is mainly dependent on the quality of

materials available for road construction, environmental conditions, proper maintenance and

available resources. The main factors for rapid deterioration of Gravel Roads include (i)

availability and suitability of gravel (ii) construction standards (iii) environmental and climatic

conditions (iv) drainage and (v) traffic. If adequate attention is not given to these factors, the

adverse effects on the performance of a Gravel Road are much more serious compared to the

performance of black-topped roads. Timely maintenance is crucial in the upkeep of Gravel

Roads. While the maintenance cost increases with traffic, still it is less compared to the

maintenance cost ofbituminous roads for low volumes oftraffic upto about 200 vehicles per day.

Gravel Roads suffer from loss ofgravel, which increases with the use ofinferior gravels and also

suffer deformation ofthe transverse profile. While deformations in the transverse profile need to

be rectified by periodic grading, excessive loss ofgravel would require frequent regravelling.

1.6.2.2. Another problem associated with Gravel Roads is the dust nuisance in low

rainfall regions, particularly when the surface gravel does not have adequate binding

properties. In many countries, dust Palliatives have been successfully used to control

dust nuisance in such situations. These aspects have been dealt with in detail in

Section 4 of this Manual. In certain situations, eventually bituminous sealing may be

warranted to overcome this problem.

1.7. Warrants for Sealing

1.7.1. Pneumatic tyred fast moving vehicles like the commercial rural vehicles damage

unprotected granular base and create dust nuisance. Also, the operating costs of such vehicles

are highly influenced by the smoothness of the road pavement. Bituminous surfacing will be

advantageous (i) where subgrade is very poor (CBR=2) and the traffic is in the range of30,000 to

60,000 ESAL applications (ii) where subgrade is poor (CBR less than 4) and the design traffic is

in the range of 60,000 to 1,00,000 ESAL applications and (iii) irrespective of the subgrade

strength, the design traffic is over 1 00,000 ESAL applications.

1.7.2. As part of the stage development strategy, it is often desirable to postpone the

provision of a bituminous surface treatment for the first few years of its service life during

which the pavement may undergo any undulations and the entire pavement system, including the

drainage system gets stabilized. Surface dressing is considered the most suitable and economical

surface treatment. It is always desirable to have some time gap between the application of first

coat and the second coat.

1.8. Potential for Large ScaleApplications and Employment Generation

1 .8.1 . In view ofthe fact that many ofour rural roads are mainly "farm to market" roads,

the design traffic is of a very low order and Gravel Roads can adequately cater to such low

volumes of traffic. After the current PMGSY targets are achieved, the remaining about 1 .7 lakh

unconnected habitations with population below 500 will generate even lower volumes oftraffic.

For such volumes oftraffic. Gravel Roads can be quite suitable.

1.8.2. The provision of Gravel Roads involving community participation can generate

tremendous employment opportunities not only for their construction but also for their

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maintenance. Furthemiore, Gravel Roads would go a long way in capacity building of small

local contractors and towards evolving appropriate technology utilizing the increasing number

of agricultural tractors for towing water bowsers and trailers, for haulage of materials, simple

implements like disc harrows for pulverization of soil clods, rotavators for blending locally

available materials and mixing ofsoil with stabilizers and water etc.

1.8.3. It is well established that the labour cost component of the total cost of the black

topped conventional pavement is much lower than the labour cost component ofthe total cost of

a Gravel Road. The construction of a Gravel Road maximises the use of locally

available materials and adoption of semi-mechanized construction techniques, thus offering

significant employment opportunities to the local communities.

Although the frequent maintenance requirements are often cited as a negative

aspect ofproviding Gravel Roads in rural areas, in fact these requirements may be considered a

big plus point in as much as they provide significant employment opportunities under various

employment generating programmes of the Central and State Governments, particularly the

National Rural Employment Guarantee Programme.

1.9. Demonstration Projects

1.9.1. Keeping in view that hardly any well-engineered Gravel Roads are being

constructed in India and that such roads are extremely popular abroad, ftill-scale

demonstration projects are warranted. If the construction and maintenance of Gravel Roads is

demonstrated in each state, such an experience would go a long way in

popularizing Gravel Roads for the low traffic volume conditions in rural areas. It is necessary to

get a feedback on the performance of well-engineered Gravel Roads, constructed under

different sets of environmental conditions. Data on road condition rating (in terms of PCI),

traffic, specific routine and periodic maintenance measures taken and their frequency should all

be recorded systematically.

2. DESIGN OF GRAVEL ROADS

2.1. Geometric Design Standards

2.1.1. Roadway width: For the single-lane gravel roads, the roadway width shall be a

minimum 7.5 m in plain and rolling terrain. However, where the traffic intensity is less than 100

motorised vehicles per day and where the traffic is not likely to increase due to

situation, like dead end etc., the roadway width shall be reduced to 6.0 m. In the mountainous and

steep terrain, the roadway width shall be 6.0 m.

2.1.2. Carriageway width: For the single-lane gravel roads, the carriageway width

shall be a minimum 3.75 m. However, where the traffic intensity is less than 100 motorised

vehicles per day and where the traffic is not likely to increase due to situations like dead end etc.

or in difficult terrain condition, the carriageway width shall be reduced to 3 .0 m.

2.1.3. Camber on carriageway: For gravel roads, the camber shall be 3.5% ( 1 in 30) for

annual rainfall less than 1 000mm and 4.0% ( 1 in 25) for annual rainfall over 1 000 mm.

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2.1.4. Crossfall on shoulders: On earthen shoulders, the crossfall should be 1%more than the camber for carriageway.

2.1.5. Longitudinal gradients: Due to the sizable proportion ofslow-moving vehicles

on gravel roads in rural areas and due to increased gravel loss on steeper gradients, it is necessary

to impose restrictions on longitudinal gradients. In plain and rolling terrain, the ruling gradient

shall be 3.5% and the limiting gradient of 5.0%, which can be relaxed upto 6%, where annual

rainfall is less than 1 000 mm. In mountainous and steep terrain, the ruling gradient shall be 5.0%and the limiting gradient of6%.

2.1.6. Horizontal alignment: The requirements of minimum radii of horizontal

curves, superelevation rates etc. for low-volume rural roads as contained in IRC:73 shall be

adopted for gravel roads. Due to the predominance ofslow-moving animal drawn cart traffic on

gravel roads in rural areas, the maximum superelevation shall be restricted to 0.07.

2.2. Materials

2.2.1. Roadmaking gravels: Roadmaking gravel has been defined as 'a mix of stone,

sand and fine-sized particles used as sub-base, base or surfacing on a road'. As per the IS Soil

Classification System,'Graver is a coarse-grained soil (with more than half the total material

coarser than 0.075 mm size), having more than halfthe 'coarse fi-action' (larger than 0.075 mm),coarser than 4.75 mm. Sand is a coarse-grained soil with more than halfthe coarse fraction, finer

than 4.75 mm. Silt and Clay are fine-grained soils with more than half the total material finer

than 0.075 mm. It is not always possible to find a suitable roadmaking gravel in a natural deposit

and often the naturally occurring gravels have to be processed to meet the specified

requirements for use in a gravel road. There are few natural deposits of material that have an

ideal gradation without being processed.

2.2.2. Grading requirements

2.2.2.1. As per the MORD Specifications, the gradation requirements of gravel/soil-

aggregate for use in base and surface courses of a gravel road are given in Tables 2.1 and 2.2

respectively. Any ofthe 3 gradings given in Table 2.1 for Base Course can be adopted depending

upon the availability ofmaterials. These gradings are recommended in case the gravel is sealed

by chip sealing or surface dressing using bituminous material.

Table 2.1 : Grading Requirements for Base Course

Sieve SizePercent by Mass Passing IS Sieve Grading Designation

A B C53 mm 100

37.5 mm 97-100 100

26.5 mm 97-100 100

19 mm 67-81 97-100

9.5 mm 56-70 67-79

4.75 nmi 33-47 39-53 47-59

425 |Lim 10-19 12-21 12-21

75 jam 4-8 4-8 4-8

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Table 2.2 : Grading Requirements for Surface Course

Sieve Size Percent by Mass Passing Designated Sieve

26.5 mm 100

19 mm 97-100

4.75 mm 41-71

425 |im 12-28

75 \im 9-16

Gravel for base courses should have very small proportion of fine materials (silt and

clay) and a relatively larger top-sized aggregate for strength and durability. Surface gravel

should have a relatively higher percentage of fines (silt and clay) and relatively smaller top-

sized aggregate, so as to readily shed offwater falling on the surface ofthe Gravel Road. Where

rounded stones are locally available, crushing ofsuch rounded stones is always suggested since

the fi-actured stones embed into the surface ofa gravel roadmuch better than rounded stones.

The percentages ofGravel, Sand and Fines (Silt and Clay) in the gradings A, B and C of

Table 2.1 are as under:

GradingA

Grading

BGrading

C

Gravel

Sand

Silt and Clay

53 to 67%

25 to 43%

4 to 8%

47 to 61%

31 to 49%

4 to 8%

41 to 53%

39 to 55%

4 to 8%

When a single naturally occurring material does not meet any of the specified

gradings, 'processing' will have to be resorted to, by blending two or more materials to achieve

the required grading.

The procedures for determining the appropriate proportioning of different materials for

achieving the prescribed grading and also to meet the requirement of Plasticity Index (PI)

have been given in Appendix-A.

2.2.2.2. Where gravel meeting the requirements in respect of grading as per the

preceding para 2.2.2.1 is not available within economic leads or cannot be economically

processed, 'Gravel' meeting the following *requirements for Base and Wearing Courses can be

used (including processing ifrequired):

(a) Base Course

Percent retained on IS 4.75 mm sieve and : 50 - 70%passing 80 mm in size

(Percent Gravel)

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Percent retained on IS Sieve 75 micron, and : 25 - 40%passing IS Sieve 4.75 mm(Percent Sand)

Percent passing IS Sieve 75 micron : Absolute max. 10%)

(Percent Slit and Clay) Desirable max. 5%)

(b) Wearing Course/Surface Course

Percent retained on IS 4.75 mm sieve and; 50 _ jqo/^

passing 80 mm in size

(Percent Gravel)

Percent retained on IS Sieve 75 micron, and . 25 - 40%passing IS Sieve 4.75 mm(Percent Sand)

Percent passing IS Sieve 75 micron . g _ ^5%(Percent Slit and Clay)

*Source : Transportation Research Board, Compendium 7 'Road Gravels'

2.2.2.3. Where gravel meeting the requirements in respect ofgrading as specified in para

2.2. 1 . and 2.2.2. is not available within economical leads or cannot be economically processed,

Soil-Aggregate mixture meeting the following requirements may be used for base and surface

courses:

Soil aggregate mixtures: Soil-aggregate mixtures may be in the form of naturally

occurring materials like soil-gravel, or soil purposely blended with suitable aggregate fractions.

The primary criteria for acceptability of such materials are plasticity characteristics and

gradation.The material should be smoothly graded for achieving the maximum possible dry

density. Fuller's grading rule {Fuller's grading rule is given by percent passing sieve = 100

(aperture size ofthe sieve/size ofthe largest particle) '} , could be used as a guide to work out the

optimum grading in different cases.A few typical gradings are given in Table 2.3. The first three

gradings indicated in this Table are especially suited for base courses whereas the remaining two

are suitable both for base course and for surfacing.

2.2.3. Plasticity characteristics offines

2.2.3.1. The requirements ofplasticity characteristics offines in surface/wearing courses

depend on the climatic conditions ofthe area. The Requirements ofLiquid Limit and Plasticity

Index offines are as under:-

Climate•

Liquid Limit(Max.)

Plasticity Index(Range)

(i) Moist temperate and wet

tropical

35% 4-9

(ii) Seasonal wet tropical 40% 6-15

(iii) Arid 55% 15-30

** Source : Low Cost Roads; UNESCO Publications. Butterworths

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Table 2.3 : Typical Grading Limits for Soil-Aggregates Mixture

Sieve Size

Percent by weight passing the sieve*

Nominal Maximum Size

80 mm 40 mm 20 mm 10 mm 5 mm80 mm 100 - - - -

40 mm 80-100 100 - - -

20 mm 60-80 80-100 100

10 mm 45-65 55-80 80-100 100

4.75 mm 30-50 40-60 50-75 80-100

2.36 mm 30-50 35-60 50-80 80-100

1.18 mm 40-65 50-80

600 micron 10-30 15-30 15-35 30-60

300 micron 20-40 20-45

75 micron 5-15 5-15 5-15 10-25 10-25

Note : Less than 10% should be retained between each pair of successive sieves specified for use

except for the pair comprising the first two sieves.

*Source : IRC : 63 - 1976

2.2.3.2. For use in base courses, the PI must not exceed 10.

2.2.4. Processing unsuitable materials: It is to be borne in mind that all types ofgravels

found in a region are not all suitable for road making, even though they classify as "Gravels" as

outlined above. In fact, there are few natural deposits that have an ideal gradation without being

processed. It is possible to take two materials, either one or both of them unsuitable alone for

highway use, and combine them to produce a granular material of satisfactory gradation. Ifthe

gradation of two available materials is known, what combinations of these materials will

produce a suitable gradation can be readily determined as per the procedure described in

Appendix-A. For many locally available materials, an effective combination may be from

crushed stone to meet the specified gradation and plasticity requirements.

2.2.5. Location and evaluation ofgravel deposits : Broadly, the procedure for location

and evaluation ofgravel deposits involves the following steps:

(a) Initial Prospecting

(i) Collect any available information in the form of Soil Maps, Geological Maps,

Aerial photographs and findings ofthe MOST Research Scheme Rl on locally

available materials in the region, local enquiries on availability ofany granular

material, rock outcrops etc.

(ii) Study any existing excavations, pits etc, and carry out a visual examination

which may warrant further investigations. Enquiries from local farmers and

residents if they have encountered any stony materials, often help in

identification ofany suitable deposits in the area.

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(iii) Study rock formations in the region. For example, in case of Igneous rocks,

any weathered granite could be a good source of gravel. In Sedimentary

rocks, there may be a possibility of gravel deposits in the form of weathered

Sand Stone and Conglomerate. Certain Metamorphic rocks with veins ofquartz

may get weathered to produce gravel. Besides, certain Limestones may lead to

the formation of calcareous aggregates like Kankar which have certain amount

of cementing action, thus showing good performance. Fig. 2.1. shows typical

quarries ofgravel.

Fig : 2.1 Typical Gravel Quarry

(b) Preliminary investigation

When the initial prospecting gives indication of possible gravel deposits at a particular

location, a number of test pits/borings should be made to demarcate the area of possible gravel

deposits. From a number ofsuch test pits/ borings, samples should be collected to determine the

quality and possible variations in the quality. For deep deposits, the variations in the quality with

depth should also be determined.A locality plan should be prepared to show the situation of the

deposit, also showing the boundaries of the deposit. The samples collected should be properly

packed and labelled (Fig 2.2). The needed laboratory tests on gradation, plasticity etc. should be

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carried out on the samples collected. Ifthe preliminary test results so warrant, the representative

samples should be subjected to detailed investigation. It should be kept in view that the

samples not meeting the requirements ofsurface or base gravel may be suitable for use in the sub-

base courses. In order to reduce the number ofsamples for detailed laboratory investigations, it is

desirable to resort to hand-feel tests in the field.

(c) Filling in sample bags (d) Tagging and marking

Fig. 2.2 : Process of Sampling

(Source : Document on Rural Road Development in India, Vol. II, CRRI, New Delhi, 1990)

(c) Detailed Investigations

When the results of preliminary investigations for a deposit are promising, detailed

investigations should be carried out. More test pits/borings need to be made on a grid system, the

spacing depending on the variability of the deposit as determined during preliminary

investigations. In each test pit/boring, the depth ofoverburden and variations in quality ofgravel

with depth should be determined. If there are variations in quality with depth, the aspect of

mixing of materials from different depths must also be considered. Further testing work should

be carried out depending on the variations in the gravel quality from the specified requirement.

The detailed investigations will be useful in estimating the quantity of gravel available, the

overburden required to be removed and variations in the quality of gravel. Other aspects to be

looked into are the work required on clearance, the haul distance to the site of work and

availability ofaccess roads for hauling the gravels to the site.

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2.2.6. Materials sampling: It is most important to get a truly 'representative'

sample to the Laboratory for testing. The main problem in getting a 'representative' sample of

aggregate/gravel is the problem of segregation. At the stockpile, there will be a tendency for the

bigger particles to roll down towards the base. It is, therefore necessary to collect samples close

to the top, middle and bottom of the stockpile (Fig. 2.3) taking care that a wooden board should

be shoved in before collecting the samples, to prevent further segregation. All the three samples

thus collected should be mixed together and the final sample for laboratory testing, reduced by

the process of 'Quartering'. Alternatively riffle box may be used to reduce total mixed sample to

the 'representative' sample for laboratory testing.

Fig. 2.3. : Sampling from Flat Stockpiles

2.2.7. Methods of testing : The standard tests commonly used to determine the

suitability of a sample of gravel as a pavement material include the following:

(i) Particle size Distribution (18:2720 Part 4)

(ii) Plasticity Index (18:2720 Part 5)

(iii) CBRTest(IS:2720Partl6)

(iv) WetAggregate Impact Value (18:2386 Part 4)

2.2.8. Handling gravel : From the time gravel is taken fi-om the quarry, the following

should be kept in view while handling gravel:

(i) Remove the topsoil or any vegetation fi-om the surface of material source before

beginning to process the materials.

(ii) Since variations in the layers of gravel are common, it is a good practice to remove

the material by working a broad area ofthe face.

(iii) To avoid the problem ofsegregation, stockpiles should be constructed in layers.

(iv) Hauling and spreading gravel should be treated as a work zone and suitable

precautions shall be taken for safety ofworkers and road users.

(v) After gravel is dropped on the road, the grader operator should place it in a

windrow.

(vi) For a new road, prior to laying gravel on a soil subgrade, the subgrade should be

properly compacted and finished to the required profile.

2.2.9. Components ofsoil-aggregate mixtures/gravels

Various constituents of Soil-Aggregate Mixtures forming gravels and their contribution

to the strength ofthe matrix are as under

(i) Gravel and Crushed Stone : Mechanical interlock and internal friction

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(ii) Coarse Sand

(iii) Medium and Fine Sand

(iv) Silt

(v) Clay

Internal friction, reduces shrinkage

Filler with slight capillary action

Adds to capillarity, produces apparent

cohesion

Low permeability; true cohesion; causes

shrinkage

2.2.10. Soil-aggregate and water interaction: Ideally, the rate of upward suction of

water from ground water below should balance the rate of evaporation from the road surface. Atypical cross-section of a Gravel Road is shown in Fig 2.4. The water interaction in the various

layers ofa gravel road can be described as under.

Layer Water Interaction

(i) Water-resisting gravel surfacing

(ii) Base course of gravel

(iii) Sub-base and subgrade

Sheds off rainwater

Utilizes suction

Conduct water to the base course

GRAVELSURFACING

SUBGRADE

GRAVEL SURFACrVG - AWELL BOUND WATER RESISTING TREATMENT ON THE SURFACE OF THE BASE

BASE COURSE - THE MAIN GRAVEL SUPPORTING THE PAVEMENT LOADINGSUB BASE -AN OPTIONAL GRANULAR LAYERSUB GRADE - 300 mm Thick Select Soil

Fig. 2.4 : Typical Cross-Section of a Gravel Road Pavement

2.2.11. Treatment with lime/cement: Under certain conditions, it is advantageous to

improve the properties of soils and aggregates by adopting soil stabilisation techniques with

small quantities of quick/slaked lime or Portland Cement. Clay soils are improved by mixing

with lime, resulting in increased strength/CBR, reduced swelling and shrinkage characteristics,

reduced water content in natural soil, better workability and improved draining properties.

Addition ofa small amount ofcement imparts cohesion between particles ofgravels and

sands. Cement can be effectively used to upgrade poor quality gravels and sands.

2.3. Pavement Design for Gravel Roads

2.3.1. General: Basically, the methodology to be adopted for the pavement design of

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Gravel Roads is the same as given in IRC:SP:72 'Guidelines for the Design of Flexible

Pavements for Low Volume Rural Roads' except that gravel/ aggregate-surfaced roads are

provided only for very low volumes oftraffic. As per this method, the design parameters include

(i) Traffic in terms ofthe number ofstandard axles (80 kN) to be carried over the design life and

(ii) Subgrade strength in terms ofCBR. These parameters are discussed in paras 2.3.3 and2.3.4.

2.3.2. Design criteria: The thickness of gravel/aggregate-surface roads shall be based

on the following criteria:

(i) the serviceability loss over the design life is limited to 2.0, taking the initial

serviceability index to be 4.0 just before opening the road to traffic, and the terminal

serviceability of 2.0 when rehabilitation will be due, with or without provision ofan

overlay.

(ii) the allowable depth ofrutting under 3 m straight edge shall not exceed 50 mm.

2.3.3. Computation of design traffic

2.3.3.1. Seasonal variations in traffic: Most ofthe rural roads being essentially farm-to-

market roads, there are significant variations in traffic volumes as observed during non-

harvesting and harvesting seasons. The seasonal variations are shown in Fig. 2.5, typically for 2

harvesting seasons ofequal duration during a year. The Annual Average Daily Traffic (AADT),

duly accounting for seasonal variations can be determinedby the simple formula given below:-

365

Where,

T = Number ofvehicles per day, including both motorized and non-motorized,

but excluding all two-wheelers, during the lean non-harvesting season.

t = Duration ofa harvesting season in days

n = Number of times by which the number of vehicles per day 'increase at the

peak harvesting season, over and above the lean season traffic T.

The values of T and n in the above formula are often readily available from local

authorities.

The use ofthe above formula is illustrated by the following example

:

Example : (i) Lean season traffic (T) = 50 vehicles per day

(ii) Duration ofa harvesting season (t) = 40 days

(iii) Traffic at the peak harvesting season increases by 5 times (i.e, n=5) to

250 vehicles per day over and above the lean season traffic of 50

vehicles per day, i.e. a total of 300 vehicles ply per day at the peak

harvesting season.

1.2 (nxT)xtAADT = T+

365

x:

"365= 5o^'-2(5x50)x40 ^

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I I I I I I I I I I I I I I I I I I ] \ I I I I I

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jon

MONTH OF THE YEAR

Fig. 2.5 : Seasonal Variations in Traffic on Rural Roads

2.3.3.2. For upgradation of existing roads: For the upgradation of an existing rural

road, ideally, the traffic census should be conducted over a period of atleast 3days, both during

the peak harvesting season and also during the lean season. However, ifthe values of t and n can

be obtained from local authorities with reasonable reliability, traffic census during the lean

season only will suffice; for lean season traffic, local enquiries can also help.

2.3.3.3. For new roads: In case of a new road, an approximate estimate should be made

of traffic that would ply on the road, considering the number of villages and their population

served along the road alignment and other socio-economic parameters. Traffic counts can be

carried out on an existing road in the vicinity with similar conditions and knowing the population

served as well as agricultural produce to be transported, the expected traffic on the new proposed

road should be estimated. Due consideration should be given to the 'Diverted' and 'Generated'

traffic anticipated as a consequence ofthe development ofthe proposed road, land use ofthe area

served, the probable growth oftraffic and the design life.

2.3.3.4.Traffic parameters for gravel base thickness design: For purposes of

pavement design, only commercial vehicles with a gross laden weight of 3 tonnes or more along

with their axle loading are considered. These include the following:

• Heavy Commercial Vehicles (HCV) comprising heavy trucks and full sized

buses.

• Medium-Heavy Commercial Vehicles (MCV) comprising medium-heavy

trucks, mini buses, tractor-trailers, pick-up vans etc.

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The design traffic is computed in terms ofcumulative number ofstandard axles of 80 kNto be carried during the design life ofthe road, using the following formula:

N = T x365x(l + O.Olry -1

Where,''''

X L X F

N = Cumulative number of standard axles for design of gravel base

thickness

T = Number of commercial vehicles per day in the year of opening the

road

r = Annual growth rate oftraffic

L = Lane Distribution Factor = 1 for single lane/ intermediate lane

n = Design Life in years

F = Vehicle Damage Factor

The parameters F, r and n are discussed in the following paras.

2.3.3.5. Vehicle damage factor: The Vehicle Damage Factor (F) is defined as the

"Equivalent number of standard axles per commercial vehicle". While the factor 'F' is arrived at

from actual axle load surveys on the existing roads, the project size and traffic volume in the case

ofrural roads may not warrant conducting an axle load survey. Therefore, indicative F values for

HCV and MCV shall be taken as 2.5 and 0.33 respectively when fiilly laden and 0.3 and 0.02

respectively when unladen. In many situations information regarding laden and unladen

commercial vehicles may not the available. The following VDF values shall be used for design

purposes, where actual data is not available:

Vehicle Type Vehicle Damage Factor

HCV 2.0

MCV 0.3

2.3.3.6. Traffic growth rate: The traffic growth rate depends upon the potential of an

area for generating traffic. In the absence ofany reliable information on this aspect, a 6% growth

rate (r) shall be taken for design purposes. The same annual growth rate of traffic shall be

considered from the year when actual field traffic surveys were carried out to the year ofopening

the road to traffic.

2.3.3.7. Design life: Normally, the gravel base thickness requirement shall be worked out

for a design life (n), of 10 years. However, depending on factors, such as the limited availability

offunds, a lower design life, not less than 5 years, shall be adopted.

2.3.3.8. Estimating design traffic parameters: In the absence of adequate data in

respect of commercial vehicles and proportions of HCV and MCV, a reasonable estimate of

design traffic in terms of cumulative standard axles during the design life of a gravel road shall

be obtained as under:

AADT* Cumulative ESAL AppUcations For 10-Year

Design Life

50 10,000

100 50,000

150 75,000

200 100,000

Includes both motorized and non-motorized vehicles, except two-wheelers.

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While pneumatic tyred carts do not need to be considered for purposes of pavement

design, it is always desirable to consider the effect of solid-wheeled (iron-rimmed)

carts in estimating traffic for pavement design. For this purpose, the correction factor

given in para 3.4.6 of IRC:SP:72-2007 shall be applied.

2.3.3.9. Traffic categories: For pavement design of gravel roads, the traffic has been

divided into three categories as under:

Traffic Category Cumulative ESAL Applications (N)

T. 10,000-30,000

30,000-60,000

T3 60,000-100,000

2.3.4. Subgrade strength

2.3.4.1. Design for new roads

2.3.4.1.1. SubgradeCBR value

For the pavement design of new roads, the subgrade strength needs to be evaluated in

terms ofCBR value.

The CBR tests should be conducted on representative samples of subgrade soil

compacted by static compaction to 100% Standard Proctor dry density and tested at a moisture

content corresponding to the wettest moisture condition likely to occur in the subgrade during its

service life. An average of test values obtained from a set of 3 specimens should be reported. If

high variations are observed in the test values from the set of3 specimens, then an average oftest

values obtained from 6 specimens should be taken.

2.3.4.1.2. Selection ofmoisture content for subgrade strength evaluation

The subgrade moisture conditions can be classified as under:-

Subgrade Classification Estimate Subgrade Moisture Content

I. Where the GWT is close enough to the

ground surface to influence the subgrade

moisture content. In non-plastic soils, GWTwill influence the subgrade moisture

content, if it rises to within Im of the road

surface; in clays oflow plasticity (PI<20), if

GWT rises within 3 m of the road surface

and in heavy clays (PI<40), if GWT rises

within 7m ofthe road surface. This category

also includes coastal areas and flood plains

where the GWT is maintained by the sea, by

a lake or by a river, besides areas where

GWT is maintainedby rainfall.

1 . The most direct method is to measure the

moisture content in subgrades below

existing pavements in similar situations at

the time of the year when the GWT is at its

highest level.

2. The subgrade moisture content for

different soil types can be estimated by

using the ratio

Subgrade Moisture Content

Plastic Limit

which is about the same when GWT and

climatic conditions are similar.

3. Where such measurements are not

possible, the subgrade strength may be

determined in terms of 4-day soaked

CBR value.

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II. Subgrades with deep GWT but where

seasonal rainfall brings about

significant changes in moisture

conditions under the road.

The subgrade moisture condition will

depend on the balance between the water

entering the subgrade through pavement

edges/shoulders during rains and the

moisture leaving the ground during dry

periods. The design moisture content can

be taken as optimum moisture content

obtained from Proctor Compaction Test

IS:2720 (Part 7) corresponding to

maximum dry density.

The Possibility oflocal perched GWTand effects of seasonal flooding should,

however, also be considered while

deciding on GWT depth. Where such

situations are encountered, the subgrade

strength may be determined in terms of

4-day soakedCBR value.

2.3.4.1.3. The Soaked CBR value ofthe subgrade can be determined by conducting CBRtests on 4-day soaked samples in the laboratory. Where adequate testing facility is not available,

typical presumptive values given in Table 2.4 can be adopted. Alternatively, soaked CBR value

can be estimated using theNomograph given in IRC :SP :72

.

Table 2.4 : Topical Presumptive Design CBR Values

Description of

Subgrade SoilIS Soil

Classification

Typical SoakedCBR Value (%)

Highly Plastic Claysand Slits

CH, MH * 2-3

Silty Clays andSandy Clays

ML, MICL, CI

4-5

Clayey Sands andSilty Sands SC, SM 6-10

Expansive clays like BC soil may have a soaked CBR of less than 2%

A simple Free Swelling Index test (IS:2720 Part 40) should be determined on

expansive clays

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2.3.4.2. Upgradation/rehabilitation of existing roads: The insitu subgrade strength of

an existing road will be determined in terms ofCBR value obtained on representative subgrade

soil samples remoulded to the insitu density at the field equilibrium moisture content, observed

after the recession of the rainy season. If, for some reason, it is not found possible to determine

the field moisture content immediately after the recession ofmonsoon, the 4 days' soaked CBRvalue of the remoulded subgrade soil samples, compacted at field moisture content to field

density, may be determined.

2.3.4.3. Subgrade strength classes : In order to use the Design Chart (Para 2.3.5), the

subgrade strength is divided into the following classes:

Quality of

SubgradeClass

Range(CBR%)

Very Poor* SI 2

Poor S2 3-4Fair S3 5-6Good S4 7-9

Very Good S5 10-15

* Where the CBR of subgrade soil is less than 2, the economic feasibility of replacing

300 mm subgrade with suitable soil needs to be explored and, if found feasible, the

pavement should then be designed based on the CBR value ofthe improved subgrade.

Alternatively, a capping layer ofthickness not less than 100 mm ofmodified soil (with

CBR not less than 1 0) should be provided.

2.3.5. Design chart: The gravel base thickness required for the five subgrade

strength classes (S,, Sj, S3, S4 and S5) and for the traffic categories ofcumulative ESAL repetitions

10,000-30,000 (T,); 30,000-60,000 (T^) and 60,000-100,000 (T3) are shown in Fig. 2.6. Achart

to convert a portion ofthe Aggregate Base Layer thickness to an equivalent thickness ofsubbase

(MORD Specifications Clause 401) with an intermediate CBR value between the base and

subgrade is shown in Fig. 2.7. It must, however, be ensured that a minimum 1 00mm thickness of

gravel base is always provided. Besides grading requirements specified for gravel base and

surfacing, the minimum soaked CBR of 80 for the gravel base material is often considered an

additional requirement. It must be kept in view that ifthe gravel base material does not meet any

ofthe two requirements (viz grading and soaked CBR value), it may not be able to withstand the

design cumulative ESAL applications over the design life, consequently requiring regravelling

earlier than designed. It may also be pointed out here that for the recommended designs to

perform satisfactorily over the design life, it is implied that all the needed routine and periodic

maintenance inputs will be provided.

2.3.6. Surface gravel: The thicknesses provided in the Design Catalogue (Fig. 2.6) are

the Gravel base thicknesses and the base gravel conforms to the requirements given in para 2.2.

Base Gravel may not form a durable crust to keep the material bound together on a Gravel Road

and is difficult to maintain. It is, therefore, recommended that the gravel base shall be covered

with the surface gravel material conforming to para 2.2. The thickness of the surface layer will

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generally vary from 40 to 50 mm depending on the traffic and quality ofmaterial. In some cases,

a running course comprising a thin loose layer ofapprox. 1 3 mm size gravel or crushed aggregate

has been provided over the surface course, acting as a cushion between the wheel load and the

pavement surface. In India, there has not been enough experience with such a running course and

should first be tried out on an experimental basis.

CUMULATIVE ESAL APPLICATIONS

SUBGRADE STRENGTH(CBR) 10,000 TO 30,000 30,000 TO 60,000 60,000 TO 1,00,000

VERY POOR(CBR = 2)

200

100

75

150

100

75

100

100

100

POOR(CBR = 3 to 4)

200275

75

100

150

FAIR(CBR = 5 to 6)

175250 275

GOOD(CBR = 7 to 9)

150 , 175 225

VERY GOOD(CBR = 10 to 15)

125 150 175

NOTE: IN SITUATIONS WHERE LOCALLY AVAILABLE/SUITABLY PROCESSED GRAVEL BASE MATERIAL FULFILLSALL REQUIREMENTS AND THEENGINEER IS SATISFIED THAT THE GRAVEL BASE MATERIAL IS WELLCOMPACTED, THE TOP 75 mm WBM LAYER MAY BE DISPENSED WITH, FOR CUMULATIVE TRAFFICUPTO 1,00,000 ESALAPPLICATIONS.

LEGEND

Dmmi

BITUMINOUS SURFACE TREATED WBM/CRMB

BASE OF GRAVEL/CRMBAVBM; CBR NOT LESSTHAN 100 (WHERE 100 mm THICKNESS IS)

RECOMMENDED, IT MAY BE MODIFIED TO 75 mmTHICKNESS FOR WBM CONSTRUCTION, WITHCORRESPONDING INCREASE OF 25 mm INSUBBASE THICKNESS).GRAVEL BASE(CBR NOT LESS THAN 80; IN EXCEPTIONAL CASES)MAY BE RELAXED SUITABLY)GRANULAR SUB-BASE(CBR, NOT LESS THAN 20; IN EXCEPTIONAL)CASES MAY BE RELAXED TO 15)

MODIFIED SOIL/IMPROVED SUBGRADE(CBR, NOT LESS THAN 10)

Fig 2.6 : Pavement Design Catalogues

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Example:

Initial Base Thickness DBSi = 27.5 cmFinal Base Thickness DBSf = 15.0 cmSubbase CBR = 30

Base CBR = 100

Solution : Subbase Thickness required = 2Qbm

Required Subbase Thickness, DSB (cm)

Fig. 2.7. Chart to convert a portion of the Gravel/Soil-Aggregate Base Layer

Thickness to an Equivalent of Subbase

(Adapted From : AASTHO Guide for Design of Pavment Structures, AASHTO, 1993)

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2.4. Drainage Design

§

2.4.1. Principles of good drainage: Since water is, beyond doubt, one of the critical

factors causing failure ofroads, the designer should aim at keeping the water away from the road-

bed. This can be achieved by following some simple principles of drainage design. They are

outlined below:

(i) The surface nin-offover the pavement surface and the shoulders should be drained

away as quickly as possible, preventing the water from finding entry into the

pavement layers from the top and into the subgrade from the top and sides

.

(ii) Precipitation over the open land adjoining the highway should be led away from the

road through natural drainage channels or artificial drains. Suitable cross-drainage

channels should be provided to lead the water across the road embankment which

may be cutting across to the natural drainage courses.

(iii) Consideration should be given to deal with the precipitation on the embankment

and cut slopes such that erosion is not caused.

(iv) Seepage and sub-surface water is detrimental to the stability of cut slopes and

bearing capacity of subgrades. An effective system of sub-surface drainage is a

guarantee against such failures.

(v) Landslide-prone zones deserve special investigations for improving drainage.

(vi) Poor embankment soils can perform satisfactorily if drainage is considered in the

design.

(vii) Water logged and flood-prone zones demand detailed consideration for improving

the overall drainage pattern ofthe area through which the road is aligned.

2.4.2. Longitudinal gradient: Despite the provision of adequate cross-slopes, slight

longitudinal drainage is necessary.Aminimum 0.3% longitudinal gradient is to be ensured.

2.43. Cross slope/camber: As specified in para 2.1.3, the crossfall/camber over the

carriageway for gravel roads should be 3.5% for low rainfall areas and 4.0% for high rainfal areas.

2.4.4. Shoulder drainage : For an efficient and quick drainage of rain water from the

roadway, it is necessary to ensure that the shoulder surface is properly sloped and is free from any

depressions or irregularities in the surface, where rainwater could get trapped.

On earthen shoulders, the crossfall should be Wo more than the camber for carriageway

(refer para 2. 1.4).

2.4.5. Roadside drains

2.4.5.1. Computation ofrun-off : All the rainfall which falls on the catchment area does

not reach the point where the drainage facility is being designed. This is due to percolation and

evaporation losses, which are governed by factors such as soil type, vegetative cover, steepness

of slope of the catchment, length of travel, temperature, land-use etc. The following formula.

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known as the Rational Formula, is generally used for calculation ofrun-off:

Q = 0.028 PI,A

Where,

Q = Maximum run-oflfincumper second

P = Aconstant depending upon the nature ofsurface

= Critical intensity of storm in cm per hour occurring during the time of

concentration

A = Catchment area in hectares

The value ofP is given in Table 2.5

Table 2.5 : Values of Coefficient of Run-off

S.No. Description of SurfaceCoefficient of

Run-off (P)

1.Steep rock and watertight pavement surface

(concrete or bitumen)0.90

2. Steep rock with some vegetative cover 0.80

3. Plateau areas with light vegetative cover 0.70

4. Bare stiff clayey soils (impervious soils) 0.60

5. Stiff clayey soils (impervious soils)

with vegetative cover and uneven paved road surfaces

0.50

6. Loam lightly cultivated or covered andmacadam or gravel roads.

0.40

7. Loam lightly cultivated or covered andmacadam or gravel roads.

0.30

8. Sandy soil, light growth, parks, gardens,

lawns and meadows0.20

9. Sandy soil covered with heavy bush or

wooded/forested areas0.10

2.4.5.2. Design of cross-section of roadside drains: When natural channels for

discharging the run-off are not available, it becomes necessary to design and construct artificial

channels. Examples ofsuch channels are:

( 1 ) Side drains in cut-sections

(2) Catchwater drains or Interceptor drains

(3) Longitudinal drains along the edge of embankment to lead run-off water to

natural channels/roadside drains /ditches

The three main types ofcross-sections for roadside drains/ditches are shown in Fig. 2.8.

Of the three shapes, the parabolic section is hydraulically the best and least subject to erosion,

even though not as easy in construction as the triangular and trapezoidal shapes. The triangular

section, although easy to construct is very much susceptible to erosion and gets easily blocked

with debris. The most commonly used cross-section is the trapezoidal section as it is acceptable

fi-om both considerations-hydraulic as well as ease ofconstruction. The side slopes should not be

steeper than 2:1, firom the view point of ease in grassing. The bottom width should normally be

not less than 0.3 m.

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TRAPEZOIDAL

Fig. 2.8 Main Types of Cross-Section

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For gravel roads, a return period ofone year is to be adopted in estimation ofrun-off For

design purposes, the storm duration should be chosen equal to the 'time of concentration'

based on the assumption that maximum discharge at any point in a drainage system

occurs when the entire catchment is contributing to the flow. The 'time ofconcentration' far from

any watershed is 'the time required for a given drop of water from the most remote part of the

watershed to reach the point ofexit' and comprises oftwo components (i) entry time and (ii) time

of flow (see Fig. 2.9). If the drainage point under consideration is at the entry of the drainage

system, then entry time is the time of concentration. If, however, the drainage point is situated

elsewhere, then time of concentration is the sum of the entry time and the time required to

traverse the length of the point under study. Fig. 2.10 gives a graph for estimating time of

concentration for catchement for different lengths, character and slope.

It is to be recognized that shorter the duration of critical rainfall, the greater would be the

expected average intensity during that period. For example, during a 60 minute rainfall,

some 10 minute period will have an average rainfall intensity far greater than for the

whole storm.

For very reliable estimation of critical intensity of rainfall, it would be ideal to have the

rain gauge records available at short intervals say 5, 10, 20, 30, 40, 50, 60 minutes.

Alternatively, the following equation can be used.

F(T+1)1 ~ T(t+1)

Where,

I = intensity ofrainfall within a shorter period of t hours within a storm

F = total rainfall in a storm in cm falling in duration ofstorm of T hours

t = smaller time interval in hours within a storm duration of T hours

The one-hour rainfall maps of India for return periods of 2, 5, 10, 25 and 50 years are

available.

For built-up areas, an entry time (or inlet time) of 5 to 1 0 minutes is normally used, but in

the case of grassy plots it may take 10 to 20 minutes for water to flow over a distance of 30 m.

This factor decreases in importance as the length ofdrain increases and entry time (or inlet time)

becomes a small proportion of the time of concentration. For a quick estimation of time of

concentration. Fig. 2.10 can be used.

The hydraulic design ofsuch channel is usually done on the basis ofManning's formula:

n

Where,

V = Velocity inm per second

R = Hydraulic mean depth

S = Bed slope

n = Rugosity coefficient

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Remotest Pointf or oreo A

Remotest point

for oreo 6

Entry timeCt)

from (4) to (3)

Areo A

'0Drain

Areo B

s\N

®

Entry time (ti)

from ® to (?)

Flow fimeCti)

from (D to (Din drain

Fig. 2.9 : Time of Concentration

Smooth 0''*Ch Bora Poor Av«ro<povement section soii turf tu,(

Tim? ot concentrotion (minutes)

Fig. 2.10 : Chart of Estimating Time of Concentration (IRC:SP:42)

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The values ofn are given in Table 2.6.

The discharge Q is then worked out using the equation:

Q=AV

Table 2.6 : Manning's 'n' And Maximum Permissible Velocity of

Flow in Open Channels

S.No. Ditch Lining Manning's 'n' Allowable velocity to

prevent erosion m/s

(1) (2) (3) (4)

1. Natural Earth

A. Without Vegetation

(i) Rock(a) Smooth and Uniform 0.035-0.040 6

(b) Jagged and irregular 0.04-0.045 4.5-5.5

(ii) Soils (Extended Casagrande classification)

V Iw U.UZZ-U.UZ<4 1 .o-Z. 1

GP 0.023-0.026 2.1-2.4

GC 0.020-0.026 1.5-2.1

GM 0.024-0.026 1.5-2.1

sw 0.020-0.024 0.3-0.6

SP 0.022-0.024 0.3-0.6

sc 0.020-0.023 0.6-0.9

SM 0.023-0.025 0.9-1.2

CL and CI 0.022-0.024 0.6-0.9

MI and ML 0.023-0.024 0.9-1.2

OL and OI 0.022-0.024 0.6-0.9

CH 0.022-0.023 0.6-0.9

MH 0.023-0.024 0.9-1.5

OH 0.022-0.024 0.6-0.9

Pt 0.022-0.025 0.6-0.9

B. With vegetation

(i) Average turf

(a) Erosion resistant soil 0.050-0.070 1.2-1.5

(b) Easily eroded soil 0.030-0.050 0.9-1.2

(ii) Dense turf

(a) Erosion resistant soil 0.070-0.090 1.0-2.4

(b) Easily eroded soil 0.070-0.050 1.5-1.8

(c) Clean bottom wit h bushes on sides 0.050-0.080 1.2-1.5

(d) Channel with tree stumps

No sprouts 0.040-0.050 1.5-2.1

With sprouts 0.060-0.080 1.8-2.4

(e) Dense weeds 0.080-0.012 1.5-1.8

(f) Dense Brush 0.100-0.140 1.2-1.5

(g) Dense willows 0.150-0.200 2.4-2.7

2. Paved

A. Concrete with all surfaces. Good or Poor

(i) Trowel finished 0.012-0.014 6

(ii) Float finished 0.013-0.016 6

(iii) Formed, no finish 0.014-0.016 6

B. Concrete bottom, float finished, with sides of

(i) Dressed stone in mortar

(ii) Random stone in mortar 0.015-0.017 5.4-6

(iii) Dressed stone or smooth concrete rubble 0.017-0.20 5.1-5.7

(Rip-rap) 0.020-0.025 4.5.

(iv) Rubble or random stone (Rip -rap)

C. Gravel bottom with sides of 0.025-0.030 4.5

(i) Formed concrete

(ii) Random stone in mortar 0.017-0.020 3

(iii) Random stone or rubble (Rip-rap) 0.020-0.0238 2.4-3

D. Brick 0.023-0.033 2.4-3

E. Bitumen (Asphalt) 0.014-0.017 3

0.013-0.016 5.4-6

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2.4.6. Surface drain linings

2.4.6.1. The need: Unlined, bare earth surfaces ofroadside ditches are highly susceptible

to erosion unless the flow is limited to a very small amount. It is, therefore, necessary that

roadside ditches are provided with protective lining which would avoid serious erosion

problems and keep them serviceable. There is a wide variety of different types of linings and the

choice of appropriate lining will depend on the site conditions. The most conmion lining which

works satisfactorily in most situations is grass.

2.4.6.2. Turfing: Grass lining is more economical than other linings to establish and with

proper maintenance, will provide adequate protection against erosion for most of the site

situations. A key factor to the success of grass lining is that it must form a firm, dense turf. For a

rapid establishment, of a vegetal lining in ditches, the same principles must be followed as

adopted for providing a vegetal protection cover on slopes. In the rainy season and in high

rainfall areas where it may be difficult to hold seeds and mulch in the ditch, an open mesh matting

of suitable material may be used instead of straw or hay mulch. The matting is laid down after

seeding and pegged with staples. Where more than one width ofmatting is required, as is usually

the case, the adjacent stripes should be overlapped (50-75 mm) and stapled at 2 to 2.5 m intervals.

It is important to ensure that matting is, elsewhere, in contact with the soil for, ifwater gets under

the matting, the seeds and soil will wash away. The efficiency of this technique depends on

making the water flow over the net, as it is matting which prevents erosion until vegetation is

established even when large amounts of rainwater flow over it. The roadside ditch can also be

lined with sod freshly cut, to a depth of about 20 mm fi*om a well established dense turf. Sod

strips should be placed across the ditch rather than length wise. The joints should be staggered

and strips pressed firmly against one another. After the sod is in place, it is tamped or rolled to

produce a smooth continuous surface. It should be watered for several weeks after placing, as

conditions may warrant.

2.4.6.3. Paved linings: Experience has shown that under two extreme site conditions on

very flat grades and then again on steep grades, the technique ofproviding grassing as a surface

lining does not always prove satisfactory. On very flat grades (less than 0.5 per cent), the flow

over a grass lining is too slow, giving rise to the problem of silting or occurrence of deposition

which is rather difficult to maintain, and, over steep grades, erosive velocities are reached,

which, due to the scouring action, can destroy the grass lining completely.

In these situations, alternative lining of cement concrete, brick/rubble masonry

especially on the internal streets passing through a village may be resorted to.

A practical concrete lining is the prefabricated type. In this construction, the panels are

cast in standard forms at a convenient central plant (Fig. 2.11).

2.4.6.4. Velocity of flow: For efficient functioning of a side ditch, the flow must be fast

enough to prevent silting or deposition but at the same time the flow must not be so fast as to

cause serious damage by scouring action. Ditches with grass lining should have a slope at least

0.5% to avoid deposition and siltation. The ditch has to have a grade steeper that ofthe roadway.

The ditch, in that case, will have to be deeper as it moves down grade and will also move farther

away fi-om the central line ofthe road, ifthe side slopes are not changed. One alternative way to

overcome the problem of silting or occurrence of deposition is to provide a secondary smaller

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channel ofV shape at the bottom ofthe ditch (Fig. 2.12) to concentrate low flow in a smaller area

of cross-section thereby increasing the flow velocity. This secondary channel sustained flow

over long periods makes it impossible to maintain grass lining, a halfpipe section may be placed

in the secondary channel.

Fig. 2.11 : Prefabricated Concrete Lining

- to be grass lined

Fig. 2.12 : Secondary Channel

2.4.7. Step-wise procedure for design of open drains: The design of the channel is

done in the following step-by-step manner.

(1) From the known soil type, arrive at the value of Manning's Rugosity

coefficient, side slopes and the maximum permissible velocity.

(2) Determine the slope from the topography.

(3) For the given discharge, calculate the hydraulic mean depth from Manning's

Formula.

(4) Find out the cross-sectional area from the given discharge and the maximumpermissible velocity.

(5) From the results of steps 3 and 4, solve the simultaneous equations to obtain the

bottom width and depth.

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2.4.8. Illustrative example: A longitudinal channel with a trapezoidal cross-section is to

be constructed in a cut section. The longitudinal slope is 1 in 250. The soil is clay, with

Mannings's Rugosity Coefficient of0.024. The maximum allowable velocity is 0.6 m/s. Designthe drain for a discharge of 0. 1 cum/s.

j:;^2/3g1/2

Solution V=

7?''^ (0.004)0.6 =

1/2

0.024

^ 0.6x0.024

0.063 ,

Discharge Q = 0.1=VxA = 0.6A

R =

V

0.024

= 0.12m

A =OA

0.6= 0.16

Perimeter P =0.16

= 1.3 mR 0.12

Taking the side slopes of the trapezoidal drain as 2 horizontal : 1 vertical

P = b+2d(l+2y = b+4.48d=1.3

Where b is the base width ofthe drain and d, the depth in metres. For a drain base width of0.3 m,the depth works out to about 0.22 m. A typicalcross-sectionofthedrainisshownin Fig.2.13

Fig. 2.13 : Typical Cross-Section for Illustrative Example

2.5. Rehabilitation of Gravel Roads

2.5.1. Rehabilitation factors: The various factors to be considered for rehabilitation

are as under :-

• Whether an overlay/strengthening layer is required or a non-overlay strategy is

appropriate

• Whethernew materials are required or the existing material can be improved upon

• Whether full reconstruction or partial reconstruction

The consideration ofthe above factors will depend on the analysis of field data collected

during 'Condition Surveys', 'Traffic Surveys' and 'Drainage Surveys.

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2.5.2. Condition survey data and its analysis: A condition survey of each gravel road

needs to be carried out at least once a year. The condition ofeach road is evaluated as 'Pavement

Condition Index' (PCI) on a rating scale of5 to 1 as detailed below:

-

(a) Based on riding comfort at 40 km/h speed

Smooth - 5

Comfortable - 4

Slightly Uncomfortable - 3

Rough and Bumpy - 2

Dangerous - 1

(b) Based on normal driving speed possible (km/h)

Normal Driving Speed PCI(km/h)

Over 35 5

25-35 4

15-25 3

10-15 2• <10 1

2.5.3. Drainage survey for rehabilitation: The condition survey data will often throw

up indications ofdistresses which are moisture related; e.g. rutting, depressions and potholes etc.

Even if such moisture-related distresses are not evident, there can exist a potential to cause such

distresses. The provisions made for drainage in the original design must be examined in order to

determine their adequacy. The longitudinal and transverse grades, width of pavement layers,

slopes and dimensions of roadside ditches etc. need to be evaluated for their adequacy. Also, a

topographic map of the area must be studied for the surface and subsurface movement ofwater.

The observations on the water level in road side ditches, collection of water on the shoulders,

over the pavement and in the adjoining area are very helpful in evaluating the drainage system.

The properties of subgrade soil, gravel base and gravel surfacing must also be evaluated as part

of the drainage survey. It is only after analyzing the drainage survey data that it is possible to

attribute the types of distresses observed in the condition survey, (as also the potential for such

moisture-related distresses to develop) to deficiencies in the drainage system.

2.5.4. Alternative rehabilitation strategies: After the collection of data fi"om the

Condition and Drainage Surveys, alternative rehabilitation strategies can be worked out

including inter alia. Reconstruction, Regravelling or Routine Maintenance.

More often than not, lack ofproper drainage ofgravel roads is the cause ofdistresses that

get manifested over gravel road surfaces. Therefore, it becomes necessary to augment the

existing drainage system. Simultaneously deficiencies in the properties of sub-base, base and

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surfacing materials may also exist, as also structural deficiencies in the thicknesses of various

layers to withstand the traffic loads. On the basis of data collected from the Condition Surveys

as well as Drainage Surveys, and considering the comparative costs of the various possible

alternatives, an appropriate rehabilitation strategy should be arrived at.

2.5.5. Selection ofmost appropriate rehabilitation strategy: As per the design criterion

for gravel roads, the performance level should not be allowed to fall below a PCI of 2.0. If,

however, proper maintenance has been neglected, the following guidelines may be followed for

rehabilitation :-

PCI Rehabilitation Measures

1 Reconstruct Immediately

1 to 2 Regravel Immediately;

Routine maintenance to continue

2 to 3 Regravel within 1 year;

Routine maintenance to continue

>3 Routine Maintenance

Overlay thickness requirement of a Gravel Road can be worked out for upgradation/

rehabilitation as per the procedure given in Para 2.3 .4.2

3. CONSTRUCTION AND QUALITY CONTROL

3.1. Choice of Technology

For rural road construction and maintenance, it is advisable to adopt an

intermediate type of technology, somewhere in between the purely manual methods on the

one hand and total mechanization on the other.

Since agricultural tractors are increasingly becoming popular in the rural areas, it would

be both suitable and economical to deploy them for rural road works by suitably

scheduling the operations between agricultural operations and road works. Figs. 3.1 and 3.2

bring out the advantages ofadopting tractor-bound technology.

The appropriate technology recommended for various task operations in rural road

development works is outlined in Table 3.1

.

35

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100 -,

MANUALMETHOD

I SEMI-

MECHANISEDMETHOD

EARTH WORK MECHANICAUY STABIUSED LIME STABIUSATION CLAYEY UME STABILISATION CLAYEYSOIL ( 70%.30% ) SOIL (5% LIME) SOIL (3% UME)

Specifications

Fig.3.1 : Unit Cost of Different Specification Using Manual andTractor-bound Tecliniques

30

23

20 .

[||.. |u im || III

00 I I

! ,5

ll l ll l l ll ll ll

10

0 J ii iiiiin iii ni , 11 lllllllllllll,

iiiiiiiiiiiHii , i i iiiiiin iii

EARTHWORK MECHANICALLY STABIUSED SOIL UME STABIUSATION CLAYEY UME STABIUSATION CLAYEY

( 70H:30% ) SOIL (5% UME) SOIL (3% UME)

Fig. 3.2: Percent Saving in Carrying Out Various Operations by Using Tractor-bound

Technology

(Source : Use of Low Cost Agricultural Implements in Low Volume Road Construction

Transportation Research Record, USA)

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Table 3.1 Choice of Technology For Rural Roads

s.

No.

Item of

Work

Tools/Equipment SuitableRecommendedTechnology for

Rural Roads

Labour

Technology

Intermediate/Semi -

iTXCdlitlllACU

Technology

EquipmentICiliCU

Technology

1. Clearing and

grubbing

Pickaxe,

Hoe, Handshovel, saw,

plough

Rippers towed by

agricultural tractor

Dozers,

Rippers

attached to

Dozers

Labour basedtechnology is

quite efficient,

generates

employment, is

cheap and hencerecommended.

2. Excavation

soil or natural

gravel for

embankment//

sub -base/

base

construction

Hoe, hand

shovel

ivippcia luwcu uy

agricultural tractor

J_/A.LaValUl,

Dozer,

Shovel,

Scraper

Labour bastpcbnnlotJV i<?i>wwixnv^ivy^^ y x.t3

quite efficient,

for the small

volume of work,generates

employment, is

cheap, and hencerecommended.

3. Excavation in

soft rock

Pickaxe,

V_.lUWUcll

Wedging

tools

Dozer,

Excavator

Labour basedtechnology is

quite efficient,

adequate for the

small volumeinvolved,

generates

employment, is

cheap, and hencerecommended.

4. Excavation in

hard rock

Handdrilling and

blasting

Air

compressor,

Jack

hammers,

and blasting

For small jobs,

hand drilling andblasting is

adequate.

For large jobs,

use of equipmentis recommended.

5. Loading and

iinlofldinp of

earth, natural

gravel , stone

materials

Shove!

Hoe

Slhovpl Hop T oaHpr Manual methodsdie di-lwLl U-dlv JLyJl

the small

quantities

involved, becauseof employmentgeneration andrelatively lowcost.

37

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Table 3.1 Choice of Technology For Rural Roads

Tools/Equipments SuitableRecommendedTechnology for

Rural Roads

s.

No.

Item of

WorkLabourBased

Technolobgy

Intermidiate

/Semi-

MechanizedTechnology

EquipmentOriented

Technology

6.Hauling of earth,

natural gravel

,

stone materials

l)Lead 0-100 mand wheel

barrow

Labour based technology

is recommended.

2) Lead 100-1000 m Pack animals Animalcart,

agricultural

tractor-

trailer,

trucks

Scraper,

Loader,

Dumper,

Trucks,

Labour based or

immediate technology is

recommended

recommended.

3) Over 1 km —Agricultural

tractor-

trailer,

trucks

Scraper,

Loader,

Dumper

Intermediate technology

is recommended

7. Spreading of soil

or pavement

materials in

layers

Hoe, Rake Blader

attachment

towed by

agricultural

tractor

Grader,

Dozer

Manual method or

intermediate technology

is recommended.

8. Breaking clods

for soil

stabilisation

Wooden Mallet Disc

harrow or

ripper

tnwpH Hv

agricultural

tractor

Disc

harrow or

ripper

towpH bv

dozer or

tractor

Intermediate technology

using agricultural

implements is

recommended.

9. Watering Watering cans Water

Browser

towed by

agricultural

tractor

Self

propelled

Water

Tanker

Intermediate technology

using a water bowser

towed by an agricultural

tractor is recommended.

lU. Mixing stablizer

like lime/cement

and soil

Hoe, rake Disc

harrow and

ripper

towed by

agricultural

tractor

Single pass

Stabliser

Intermediate technology

using agricultural

implements towed by

agricultural tractor is

recommendedbecause of its low cost.

38

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s.

No.

Item of

Work

Tools/Equipments Suitable

RecommendedTechnology for

Rural Roads

LabourBased

Technolobgy

Intermidiate/Semi-

MechanizedTechnology

EquipmentOriented

Technology

11. Production of

stone aggregates

1) For Water

Bound MacadamHammer Mobile

crushing

plant with

manual

loading

Crushing

Plant with

screens,

conveyors

and

loaders

Manual breaking of

stones is recommended

for small jobs.

For larger jobs, small

mobile crushing plants

are recommended.

2) For Wet MixMacadam,Concrete and

bituminous

surfacing

Not

recommended

Mobile

crushing

plant with

manual

loading

CrushingPlant

screens,

conveyors

andlofidprs

Intermediate Technology

using mobile crushing

plant and manual loading

is recommended.

12

earthwork sub -

base, WBM and

aggregate base

Rollers pulled

by animals or

human labour

8/10 t

Static

Smooth

Wheel

Roller

Vibratory

Roller8/10 t Static smooth

wheel roller is

recommended.

13. Prime Coat/

Tack Coat

Hand held

cans with

Hand held

lance

JUIU VIUCVJ

with a

sprayer,

operated

by

compressor

Self

propelled

XJllUlllCll

Pressure

Distributor

Intermediate technology

using hand held lance

with a sprayer and

operated by compressor

or hand pump is

recommended

14. Application of

binder for

surface dres sing

11 H Tviiil cir^n1f XZfillUioiiJll

Hand held

cans with

holes

Hand hHH

lance with

sprayer,

operated

by

compressor

Self

propelled

Bitumen

Pressure

Distributor

Hand held lance with

sprayer, operated by

compressor or hand

pump is recommended.

ii) 80/100 Pen.

WlaUC Dl lUinCIl

ndllU ilCiU

cans with

holes

XTctiXCl ilClLX

lance with

sprayer,

operated

bv

compressor

propelled

Bitumen

Pressure

Distributor

Hand held lance with

sprayer, operated by

compressor or hand

pump is recommended.

15. Heating Bitumen Bitumen

Boiler of

Small

capacity

Bitumen

Boiler of

small

capacity

High

capacity

Bitumen

tanks

Bitumen boiler of small

capacity is

recommended.

39

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s.

No.

Item of

Work

rip ^ I „ /T7Tools/Ec uipments Suitable

RecommendedTechnology for

Rural Roads

LabourBased

Technolobgy

Intermidiate/Semi-

Mechanizedlecnnoiogy

EquipmentOriented

Tpchnnlnov-1.VvillivlUgY

16. Bitumen Premix

Carpet

Not

recommended

Mini-Hot

Mix Plant

of6t

capacity

Mobile

Hot MixPlant of 20

t capacity

Mini Hot Mix Plant of

6 t capacity is

recommended.

17. Application of

chips for surface

dressing

Manual, by

basket, and

spreading by

rakes

Spreader

box towed

by

agricultural

tractor

Sell

propelled

Chip

spreader

Mannual or intermediate

technology is

recommended.

18. Laying of

Premix Carpet

Manual, by

rakes

Manual by

rakes

Paver

FinisherMannual spreading by

rakes is recommended.

19. Rolling of

i) Chips for

surface dressing

Handoperated

Roller

Not

recommended

8/10 t

static

smooth

wheel

roller

8/10 t

static

smooth

wheel

roller

8/10 t staic smooth

wheel roller is

recommended.

ii) Premix Carpet Not

recommended

20. Production of

Cement Concrete

Hand mixing

Not

recommended

Small

concrete

mixers,

with

weighing

facility

Small

Batching

Plants

Small concrete mixers

with weighing facility

are recommended

21. Vibration of

concrete

Rodding

Not

recommended

1 Needle

vibrators

2 Screeds

for concrete

pavement

3 8/10 t

Roller for

Roller

CompactedConcrete.

1 Needle

vibrators

2 Screeds

3 Vibratory

Roller for

Roller

CompactedConcrete.

1 Needle vibrators for

RCC slabs, beams,

mass concrete.

2 Screeds for concrete

pavement.

3 8/10 t static roller or

vibratory roller for

Roller Compacted

Concrete.

(Source : KadiyaH, Dr. L.R and Lai, Dr. N.B 'Principles and Practices of HighwayEngineering Khanna Publishers, New Delhi, 2006)

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3.2. Plant Selection and Usage

Table 3.2 gives the plant/equipment considered appropriate and economical for various

field operations in the construction ofgravel roads.

Table 3.2 Appropriate Plant/Equipment for various Field Operations

Construction Operation Appropriate Plant/Equipment

i) Clearing, Grubbing and Excavation.

ii) Hauling of Earth

iii) Spreading of soil/gravel in layers

iv) Adding water to soil

v) Mixing of soil with water

vi) Mixing of different locally available materials

for mechanica I stabilization

vi$ Pulverization of soil clods

vii) Mixing of stabilizer (lime or cement) and water

with soil.

ix) Compaction

Ripper towed by agricultural tractor.

Agricultural tractor-trailor.

Blade attachment towed by agricultural tractor.

Water Bowser towed by agricultural tractor.

Agricultural tractor towed disc harrows.

Agricultural tractor towed Rotavator.

Agricultural tractor-towed disc harrows.

Agricultural tractor-towed Rotavator.

80-100 kN Static smooth-wheeled Road Roller.

3.3. Sequence of Construction Operations : First and foremost in the sequence of

construction operations is the site preparation, as per specified procedure. After site preparation,

the cross drainage works (culverts, causeways etc.) and the surface drains need to be provided as

per the Drainage Plan requirements. The Earth work and Subgrade preparation are then taken up,

(discussed in para 3.4). For a sub-base course, where required to be provided, the materials to be

blended are placed in the required proportions, mixed thoroughly and spread to the desired

thickness and shape, (para 3.5). After compacting the sub-base, the materials to be blended for

the gravel base are placed in the required proportions, mixed thoroughly, spread to the

required loose thickness and shape and compacted to the desired density. The compacted gravel

base is finished to the desired profile (described in para 3.6). Thereafter, a gravel surface course

is laid, compacted and finished to the desired profiles.

3.4. Earthwork and Subgrade Preparation

3.4.1. Earthwork

3.4.1.1. The cost of earthwork generally constitutes 40 to 60% of the total road

construction cost. It is, therefore, essential that careful consideration is given towards site

planning and various operations involved in the execution ofthe earthwork for economizing the

cost of road construction. Since gravel roads are often upgraded later to black-topped flexible

pavement standards as the traffic grows, it is both difficult and uneconomical to make up any

deficiencies in earthwork at a later stage, pointing to the need for strictly adhering to the

specifications laid down in Clause 30 1 ofMORD Specifications. The main activities involved in

earthwork operation are:

(i) Soil survey and laboratory investigations for suitability of material and for

determining theCMC andMDD ofembankment material compaction

(ii) The construction ofembankment.

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3.4.1.2. Test pits should be dug in borrow areas from where the embankment materials

are to be obtained and representative samples tested for determining their suitability as a fill

material as per the requirements laid down in Clause 301.2.3 of MORX) Specifications.

Ordinarily borrow pits along the road should be discouraged. Where permitted by the Engineer,

the requirements laid down in Clause 30 1 .4. 1 ofMORX) Specifications must be complied with.

3.4.1.3. Prior to the construction operations, the formation for embankment construction

should be prepared as laid down in Clause 301.4 of MORD Specifications. The various

construction operations should be carried out as per Clause 301.5 ofMORD Specifications. The

soil for embankment construction at the time of placement should be at proper moisture i.e.,

(+)2% ofOMC. Additional water should be added ifrequired and the soil should be turned 2 to 3

times so that the water is quite uniformly dispersed. In case the soil contains excess moisture, the

soil should be allowed to dry to bring it the optimum before compaction.

3.4.1.4. For earthwork filling, in layers, the compacted thickness ofthe soil layer should

not exceed 1 50 mm when static smooth wheeled rollers of 80 to 100 kN static weight are used.

When the earthwork has reached a stage when the general form of the final shape of the

embankment has been obtained, the spreading ofthe earth should be done, in straight reaches, to

a crowned shape, and to appropriately superelevated profile if the reach is on a curve. The

moisture content in the laid soil should be the optimum moisture content subjected to the

permitted tolerance. Highly expansive soils such as black cotton soil should be compacted at the

specified moisture content. The clods should be broken to less than 75 mm size. The equipment

for compaction should ordinarily be a 80-100 kN tonne smooth-wheeled power roller. For the

control ofmoisture prior to compaction, a truck mounted water tanker should be used, but in the

absence ofsuch a water tanker, a tractor-towed waterbowser could be used (Fig 3.3).

Fig. 3.3 : A Tractor-towed Water Tanker for Control of Moisture Prior to Compaction

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3.4.1.5. The tolerance limits of variations from the specified moisture content are

normally ±2% ofOMC. Densities to be aimed at in the compaction process shall be chosen with

due regard to factors such as soil type, height of embankment, drainage conditions, position of

individual layers, and type of available compaction plant, in accordance with Clause 301 of

MORX) Specification. Each compacted layer shall be tested in the field for density, and accepted

before operations for the next layer commence. The field density in the body of the

embankment shall not be less than 97% of standard Proctor density and 100 percent in the top

300 mm of the embankment (Subgrade). Expansive clay (such as black cotton soil) possessing

high volumetric changes should be compacted at a moisture content, wet ofthe optimum and to a

density not exceeding 90 percent of the laboratory standard Proctor density. The overall profile

should be improved with each successive layer so that as the subgrade level is approached, the

profile ofthe formation is as per lines and grades.

The related quality control requirements are detailed in the Quality Assurance

handbook for Rural Roads, 2007.

3.4.2. Subgrade preparation: The top ofembankment which is to receive the hard crust is

called subgrade. The subgrade soil layer shall preferably be made from good soil available

locally. The soil shall be free from vegetative matter and rubbish. In case the reach is at grade or in

cutting and insitu soil is to be used for subgrade, the method consists in loosening the soil to 300

mm depth, bringing the moisture to proper value and compacting it with a suitable roller to

maximum Proctor density. The compaction process should commence at the edges and progress

towards the center. When the reach is in filling, it is necessary to ensure that atleast the top 300

mm of the embankment constituting the subgrade of the pavement should be compacted to 1 00

percent Proctor density in two layers at controlled moisture. The subgrade should be finished to

the desired profile; a camber board should be used to check the cross profile (Fig. 3.4).

The related quality control requirements are detailed in the Quality Assurance

Handbook for Rural Roads.

3.5. Sub-Base Construction

In Gravel Roads, generally a gravel base of required thickness, as per the Design

Catalogue, Fig.2.6 in Section 2, is provided directly over the subgrade, except for the very weak

subgrade (CBR=2), where a capping layer is provided. However, a part of the gravel base

thickness can be converted into a subbase (Fig. 2.7, Section 2) layer having a CBR value in

between the CBR values of the subgrade and the gravel base. The sub-base can be a Granular

Sub-base (GSB) as per Clause 40 1 ofMORD Specifications or Lime-treated soil sub-base, as per

Clause 403 of MORD Specifications or Cement-treated soil sub-base as per Clause 404 of

MORD Specifications, depending on the locally available materials. The salient features of

construction ofthe above three types ofsub-base courses are outlined in paras 3.5.1, 3.5.2 and

3.5.3 below.

3.5.1. Granular sub-base: Where the locally available materials meet the grading,

plasticity and other requirements as laid down in Clause 401 of MORD Specifications, these

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— LIFTING HANDLE

(a)

LIFTING HANDLE

PAVEMENT SURFACE

DETACHABLE WOODENPROFILE BOARD

Fig. 3.4 : (a) and (b) Two Designs of Camber Board

materials can be used directly without any processing'. However, where the locally available

materials do not meet the various requirements without any processing, the following

mechanical stabilization techniques can be resorted to:

(a) Stabilization of clay with sand, involving the mixing of clay with sand so

that the resulting mixture will have controlled plasticity (PI < 6) and

minimum 30% sand content. The clay shall be excavated and clods broken

by 4 to 6 passes of tractor-towed disc harrows (Fig. 3.5) to meet the specified

pulverization requirements. The soil should be spread in place to the

required loose-thickness. The requisite quantity of sand transported from

local sources is then added. The required quantity of water is added to bring

the moisture content to the optimum. Depth blocks should be used for the

control of required layer thickness (Fi.g 3.6). The mix should then be

compacted by 80 to 1 00 kN smooth-wheeled roller to 100% Proctor density.

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(b) Stabilization of soil with soft aggregates (such as brick bats, kankar and

laterite) is similar to the mechanical stabilisation of clay with sand as at (a)

above. The soft aggregates to be added to the blended soil mixture shall be

V, of size less than 30 mm and have wet AIV not more than 50%. The blended

soil and aggregate should be mixed together in the ratio 7:3 by volume.

(c) Soil-Gravel/Soil-Moorum mixes shall contain a fair proportion of all

particle sizes together with sufficient clay to provide proper cohesion as per

technical grading limits. The maximum aggregate size should not exceed

one-third the thickness of stabilized layer. The construction shall otherwise

be carried out in the same manner as for other mechanically stabilized soil

construction. Care should be taken that the layer is thoroughly compacted

and laid to proper profile.

3.5.2. Lime stabilized soil construction

The specification for lime stabilized soil construction shall apply essentially to

stabilization of alluvial soil, moorums, clays and black cotton soils. As mentioned earlier, the

borrow areas may be previously watered for easy excavation. The excavated soil shall be

pulverized, so that all soil clods pass the ISS 26.5 mm sieve and more than 80% through ISS 4.75

mm sieve using tractor-towed disc harrows. In case ofblack cotton soil, the borrow areas shall be

previously watered and the clods which are generally in the size range of 1 00- 1 50 mm should be

pulverized with agricultural equipment (disc-harrows), and Rotavator (Fig. 3.7). The pulverized

soil (alluvial/moorum/ black cotton soil) shall be spread on the prepared receiving surface, and

slaked lime spread over it in the required quantity (Fig. 3.8) as per the guidelines provided in

Clause 403 ofMORD Specifications. For the safety ofworkers, hand gloves should be provided

while handling lime. The laid material shall be cut and mixed thoroughly, using a

tractor-towed Rotavator. The mass shall then be spread to the required loose

thickness to proper profile. The compacted thickness of a layer shall not exceed 1 50 mm if 80-

1 00 kN smooth wheeled roller is used. The laying width shall extend by 150 mm on either side,

beyond the pavement width on top. The layer shall then be thoroughly compacted without much

delay (within 3 hours) after mixing with lime with a 80- 1 00 kN smooth-wheeled roller giving 6-8

coverages as for earthwork. The subbase layer shall be checked for compaction. All controls and

permitted tolerances shall be as given in Clause 403 ofMORD Specifications. The surface after

compaction shall be cured for 7 days by sprinkling water periodically, covering by wet gunny

bags (Fig. 3.9) soon after which subsequent pavement courses shall be laid to prevent the surface

from drying out and becoming friable. The traffic shall not ply directly over the stabilized layer

during the period of curing. The related quality control requirements are detailed in the Quality

Assurance Handbook for Rural Roads.

3.5.3. Cement stabilized soil construction

For cement stabilized soil construction, the various construction operations and the

equipment deployed are essentially the same as for lime stabilized soil construction except that

compaction should be completed within 2 hours after mixing.

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Fig. 3.9 : Curing by Covering the Compacted Stablized Soil Surface with

Wet Gunny Bags

3.6. Gravel Base/Surface Course Construction and Quality Control

While detailed specifications are contained in clause 402 ofMORD Specifications, the

salient features ofthe Methodology to be adopted and the Quality Control requirements are given

below:

A. METHODOLOGY

1. The Gravel/Soil-Aggregate in base and surface course shall meet all the

physical requirements set forth in Para B and conform to the gradings given in Table

2.1 of Section 2 for base course and in Table 2.2 ofSection 2 for surface course.

2. Before receiving the Gravel/Soil-Aggregate material, the subbase/base, as the case

may be, shall be prepared to the specified lines and crossfall. Any existing ruts,

predominant irregularities or soft yielding places should be corrected and rolled

until a firm surface is obtained.

3 . The Gravel/Soil-Aggregate material meeting all the specified requirements shall be

spread on the prepared surface with the help of a grader of adequate capacity, for

maintaining the required slope and grade.

4. Where com.bination of different materials is required for obtaining the

Gravel/Soil-Aggregate meeting the specified requirements, mixing shall be done

mechanically by the mix-in-place method.

5. The equipment for mix-in-place shall be a tractor-towed rotavator or similar

equipment capable ofmixing the materials to the desired degree.

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6. It must be ensured that prior to compaction, the moisture content is within 2 percent

of the optimum moisture content, making due allowance for evaporation losses.

After adding the required quantity of water, the material should be processed bymechanical means like tractor-towed disc harrows/rotavators until the layer is

uniformly wet.

7. Rolling shall be carried out as per Para 402.4.2 ofMORD Specifications.

8. The density to be achieved should be 100% of the maximum dry density for the

material determined as per IS:2720 (Part 7).

9. Any loose, segregated or otherwise defective areas should be made good to full

thickness oflayer and re-compacted.

B. QUALITYCONTROLREQUIREMENTS

1 . Materials

(i) The grading for Gravel/Soil-Aggregate Base shall conform to the requirements

given in Table 2.1 of Section 2 while the grading for Gravel/Soil-Aggregate

Surface Course shall conform to the requirements given in Table 2.2 of Section 2.

(ii) Wet Aggregate Impact Value (IS:5640) shall not exceed 40 and 30 when used in

base and surfacing respectively.

(iii) The needed gradation shall be obtained by crushing, screening and blending

processes as necessary.

(iv) Fine aggregate material passing 4.75 mm sieve shall consist ofnatural or crushed

sand and fine mineral particles.

2. HorizontalAlignment

The edges of the Base shall be correct within a tolerance limit of (+) 30

mm in plain and rolling terrain and (±) 50 mm for hilly areas. The edges of the

carrigaeway with Gravel/Soil-Aggregate Surfacing shall be correct within (±) 20

mm in plain and rolling terrain and (±) 30mm in hilly terrain.

3. Surface Levels

The tolerance in surface level for Gravel/Soil-Aggregate Base and

Surface will be restricted to (±) 10 mm. A grid of 10 m by 2.5 m may be

formed to check the surface level.

4. Surface Regularity

The maximum permitted difference between the Gravel/Soil-Aggregate

layer and 3 m straight edge shall be 1 2 mm for longitudinal profile and 1 0 mm for

cross profile. The cross profile should conform to the prescribed camber.

5. Degree ofCompaction

Density shall be 100 per cent ofmaximum dry density for the material determined

asperIS:2720(Part7).

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6. Quality Control Tests

The quality control tests and their frequency for gravel/soil-aggregate base and

surface construction shall be as per Tables 3.3, 3.4 and 3.5, as laid down in the

QualityAssurance Handbook for Rural Roads.

Table 3.3 : Quality Control Tests Prior to Construction

Type of Test Frequency

1. Soil Classification as per IS: 1498.

1 . Wet Sieve Analysis, except for cohesionless soil.

2. Liquid Limit and Plastic Limit

One test from each source identified

by the Contractor.

2. Combined Grading and Plasticity tests on materials

from different sources, mixed in the design proportions.

This shall be done when materials from more than one

source are combined.

One test on the combined material.

3. Proctor compaction Test (IS:2729 Part 7) One test on the material from each

source or on the combined material,

as the case may be.

4. Wet Aggregate Impact Value Test (IS: 5640) where

soft/marginal aggregates are used e.g., Laterlite,

Kankar etc.

One test from each source identified

by the contractor.

5. CBR test (IS:2720 Part 16) on representative sample

compacted at 100% Proctor dry density.

One test per km length.

Note : Where materialsfrom more than one source are to be combined in the desired

proportions, the tests at SI. Nos. 2, 3 and 5 should be carried out on the combined

material.

Table 3.4 : Quality Control Tests During Construction

Type of Test Frequency

1. Wet Sieve Analysis (18:2720 Part 4) on the

GSB material combined in the design

proportions from various sources

Atleast one test to be carried out

daily.

2. Liquid Limit and Plastic Limit tests (IS:2720

Part 5)

-do-

3. Placement Moisture Content (IS:2720 Part

2)

Atleast 3 tests to be carried out

daily, well spread over the day's

work.

4. Insitu Density measurements (18:2720 Part

28)

-do-

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Table 3.5 : Quality Checks by AE/EE

Stage Test Frequency

Designation

of

Inspecting

Officer

1 . Top of the First

Layer before

placing the next

Gravel layer

i) Degree of

Compaction

(IS:2720 Part 28)

i) Minimum 3 tests for each

km length or part thereof;

ii) Individual test values of the

degree of compaction

attained shall not be less

than 1% of the specified

degree of compaction. For

example, for the required

degree of compaction of

100% Proctor Density, the

individual test values shall

not be less than 99% of

Proctor Density and the

average of three (or more)

tests carried out in a day

allali IlUl UC less llldll iUU/0

Proctor Density).

AE

AE

ii) Surface

Regularity and

Transverse Profile

Random Checking AE

Z,. iT llllSllCU. VJlctVCl

Layer

ij L-'CglCC Ui

compaction

(IS:2720 Part 28)

Ij WllC LC^l iUl CctCll Z,JU ill

length or part thereof

length or part thereof

AF

FF

ii) Surface

Regularity and

Transverse Profile

Random Checking AE

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C. DO'S AND DON'TS

1.

Do's

While preparing the subbase/ base, where

predominant irregularities exist, make sure that

the surface profile is corrected before spreading

the Gravel/ Soil-Aggregate Mix.

For the equipment used for mix-in-place

construction, carry out trial runs to establish the

suitability for the work.

Look for soft patches, ifany and rectify them by

removing or adding fresh material and

compacting the same throughly.

For obtaining the needed uniformly ofmixing of

water with Gravel/Soil-Aggregate, sufficient

passes of mechanical equipment like tractor-

towed disc harrows/ rotavators should be

ensured.

Adopt Tractor-Bound Technology, using the

local agricultural tractors.

Make sure that the earth used in the earthen

shoulders has the requisite properties and is

compacted to 100% Proctor Density and that

proper cross slopes ( 1% steeper than camber)

are provided.

3.

5.

Don'ts

Do not permit any organic or

deleterious material.

Do not allow manual mixing,

unless the width of laying is not

adequate for mechanical operations,

as in small-sizedjobs.

Do not allow the speed of the roller

to exceed 5 km per hour.

Do not allow sharp turns with the

compaction equipment because

they can cause surface roughness.

Do not leave the side slopes

un-turfed, otherwise rain cuts

would be formed.

Do not forget to provide a well-

designed drainage system, with

properly identified outlets.

3.7. Providing Gravel Surface

Over the finished base course, a gravel surfacing material meeting the specified

requirements given in Chapter 2 is spread to the required loose thickness, compacted to the

required density and finished to the desired profile.

It is good practice to place a thin layer of about 12 mm size broken stone or gravel. This

layer is intended to act as a "Cushion" between the wheel load and the base course. It is supposed

to absorb some ofthe abrasive forces ofa passing wheel. The use ofthis thin layer is optional, but

in many cases it has been noted that ifa running course is not separately provided, it will develop

naturally on its own. In light grading, the motor grader or drag works on the running course and

thus does not cut into the base course with its water resistant crust. If maintained evenly spread

over the carriageway, then the rest ofthe pavement should last a long time and should not dry out

very quickly in dry weather.

In general, running course is a protection against erosion caused either by climate or

vehicle loadings.

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3.8. Sealing a Gravel Road

3.8.1. Before applying bituminous surface treatment, any existing surface gravel with a

PI exceeding 10 shall be scarified and removed and the existing surface brought to proper

transverse profile. Any irregularities in the longitudinal and transverse direction must be

removed. If any granular layer overlay is required, the same should be implemented. Prior to

applying the bituminous treatment, the prepared gravel surface must be primed by spraying a

Slow Setting Bituminous Emulsion with a kinematic viscosity of250-500 Centistokes at 60''C at

the rate of 1 2- 1 5 kg per 1 0 sqm area. Surface Dressing is considered a preferred surface treatment

for low volume rural roads. The selection of the size of stone chippings should be based on the

anticipated traffic and the type of surface to be provided with the bituminous surface treatment.

The design of surface dressing may be done in accordance with the design procedure

recommended in IRC: 11 0-2005 Standards specifications and Code of Practice for Design and

Construction ofSurface Dressing.

3.9. One-Coat and Two-Coat Surface Dressing

3.9.1. Whether one-coat or two-coat surface dressing is to be provided on a rural

road shall be decided on the basis of anticipated traffic and climatic conditions.

3.9.2. The cover material shall consist ofcrushed stone, crushed gravel (shingle) or other

stones. It should be clean, strong, durable and of fairly cubical fragments, free from disintegrated

particles, vegetable matter, dust and adherent coatings.

3.9.3. The surface dressing work shall preferably be carried out when the atmospheric

temperature in shade is lO^C or above. The bituminous material shall not normally be applied

when the surface or the cover material is damp, weather is rainy or during dust-storm. The

underlying course on which surface dressing is to be laid shall be prepared, shaped and

conditioned to a uniform grade. The surface should be swept clean free of caked earth and other

foreign matter with hard brushes, then with softer brushes and finally blown off with sacks or

gunny bags to remove fine dust. When the base to be treated is gravel or stabilized soil, a

bituminous primer coat shall be applied uniformly at the specified rate. After priming the base,

the bituminous binder shall be spread at the rate determined as per IRC: 11 0-2005. Immediately

after the application of bituminous material (Fig. 3.10) the cover material shall be spread in

required quantities by suitable means so as to cover the surface completely. The surface shall be

broomed to ensure uniform spreading.

3.9.4. The entire surface shall then be rolled immediately after the application of cover

material with a suitable roller. The rolling shall begin at the edges and proceed towards center,

except on the super-elevated portions, where the rolling should proceed from the inner to the

outer edge. Additional aggregates shall be spread in whatever quantities may be required to fill

irregularities and to prevent picking up ofthe aggregate by the roller.

3.9.5. The finished surface shall be opened to traffic on the following day. Ifunder some

special circumstances, the road has to be opened to traffic immediately after rolling, speed of

traffic shall be limited to 1 6 km per hour until the following day.

3.9.6. The quahty of materials, construction etc. for two coat surface dressing shall be

similar to one coat surface dressing. Prior to the application of second coat, the surface shall be

cleaned properly. Binder, heated to appropriate temperature, shall be sprayed, preferably with a

mechanical sprayer, at the specified rate.

3.9.7. Immediately after the application of binder, the cover material shall be spread

by suitable means at the specified rate to cover the surface completely. The rest of the process

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of rolling, finishing and opening to traffic shall be similar to one coat surface dressing.

(a) Spraying Bituminous Material over Prepared Surface

(b) Spraying Cover Material

Fig. 3.10

3.10. Step-wise Procedure for One-Coat and Two-Coat Surface Dressing

(a) The material viz. aggregates and binder should be checked for specification

requirements.

(b) All depressions and pot holes etc. on the receiving surface should be corrected.

(c) The receiving surface should be cleaned by brushing to ensure that there is no

loose material before binder is applied.

(d) If bituminous primer coat is applied, it should be cured before laying surface

dressing.

(e) No surfacing work shall be carried out if-

(i) atmospheric temperature in shade is less than 1 0°C or

(ii) base is damp or

(iii) construction materials are damp or

(iv) the weather is foggy, rainy or dusty;

(f) The work should be so organized that no traffic or dust gets on to the cleaned or

bitumen painted base.

(g) The rate of spray of binder should be regularly checked using tray method. Theends of the stretch should be covered with thick paper so as to avoid double

spraying of binder. The temperature of binder at the time of application should

also be checked.

(h) Immediately after application of binder, the aggregates should be uniformly

spread; ifneeded, use brooms for spreading.

(i) The rolling on aggregates with approved roller shall commence immediately

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from the edges progressing gradually towards the center parallel to the center

line. At super-elevation, it should proceed from inner edge to outer edge,

(j) Rolling operations should be continued till aggregates are firmly embedded in

binder.

(k) Second coat, ifspecified, can be laid after 2 to 3 weeks.

(1) Finished surface should be checked for cross and longitudinal profiles using 3 mstraight edge.

(m) No traffic should be allowed for 24 hours. If cutback/emulsified bitumen is

used, the finished surface should be closed to traffic till the binder is adequately

cured/set.

3.11. Step-wise Procedure For Providing 20mm Bituminous Premix Carpet

(a) The materials viz., aggregates and bituminous binder should be checked for

specification requirements.

(b) The underlying surface on which the bituminous surfacing is to be laid should

be suitably prepared, with all depressions and potholes etc. corrected, shaped

and conditioned to the specified lines, grades and cross-sections.

(c) The receiving surface should be cleaned by brushing to ensure that there is no loose

material on the surface.

(d) A prime coat where needed should be applied as per specified procedure, using

hand held lance provided with a sprayer, operated by compressor. Use of hand

held cans with holes should not be permitted.

(e) Tack coat should be applied at the specified rate uniformly on the prepared

base, using hand held lance provided with a sprayer, operated by compressor.

(f) Mixing of aggregates and bitumen in specified quantities should be carried out

in a Mini Hot Mix Plant of preferably around 6 t/hour capacity, carefully

controlling the specified temperature of heated aggregates and bitumen and the

mixing temperature.

(g) The hot mix should be immediately transported from the mixer to the point of

use in suitable vehicles or hand barrows. The vehicles should be clean and the

mix being transported should be covered in transit.

(h) The pre-mixed material should be spread even to specified thickness and

camber, making due allowance for any extra quantity required to fill up

depressions. The cross-fall should be checked by camber boards and any

irregularities leveled out.

(i) Rolling should begin at the edges and progress towards the center

longitudinally, except that on superelevated and uni-directional cambered

portions, it should progress from the lower to upper edge parallel to the center-

line. Wheels ofthe roller should be kept moist.

(j) Rolling should be continued until the entire surface has been rolled and all

roller marks eliminated,

(k) A seal coat where specified should be applied to the surface immediately after

laying the surfacing.

(1) The finished surface should be checked for line, level and regularity using

camber board/straight edge

.

(m) Traffic may be allowed on the surface once it has reached ambient temperature,

but speed must be rigorously restricted to not more than 1 6 km per hour.

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4. MAINTENANCE METHODS AND MANAGEMENT SYSTEM

4.1. General

4. 1.1.While proper maintenance of all types ofroad pavements is important, it is a matter

of crucial importance for the satisfactory performance of Gravel Roads. Even though Gravel

Roads require more frequent maintenance interventions than black-topped roads, these

interventions are relatively inexpensive and simple, within the available resources and skills in

rural areas. Specially designed studies as well as experiences all over the World show that for low

volumes of traffic upto about 200 vehicles per day, the maintenance costs of gravel roads work

out to be lower than for black-topped roads, while for higher volumes oftraffic, it is the other wayround. It is mainly the neglect of proper maintenance that is responsible for gravel roads not

gaining popularity in the vast rural areas of India with low to very low volumes of traffic. With

simple inexpensive maintenance interventions, gravel roads can be easily maintained in good

condition. The simple and labour intensive maintenance methods also hold considerable

potential for employment generation.

4.1.2. Causes of deterioration : A gravel road deteriorates in its level of service ability

with age, basically due to following factors:

(a) Traffic: The traffic operating on the facility can cause different types ofdistress like

rutting, corrugations, loss of materials, and structural deformation. The extent of

deterioration depends upon the intensity of traffic, especially the wheel load and its

repetitions. Solid-wheeled cart traffic can be very damaging to the road, since the

solid wheels cut into the pavement causing deep ruts.

(b) Environment: The external influence of environmental factors such as rainfall and

snowfall, can also cause deterioration of the pavement. Rainfall causes erosion of

shoulders and slopes and ingress ofwater into the pavement structure and subgrade

and affects the performance of drainage structures. Snowfall can cause ingress of

moisture into the pavement structure and subgrade and result in frost action. The

influence of the environment on a gravel road is much more severe than on black-

topped/ concrete roads.

4.1.3. Maintenance operations

(a) The various maintenance operations on gravel roads can be broadly classified into

the following categories :-

(i) Routine maintenance, comprising patch repairs; dragging, grading,

maintenance of shoulders and repairs to roadside drains, road signs, culverts

etc., and collection of data such as road condition and traffic surveys, which

are required to be carried out by the maintenance staff once or twice every

year.

(ii) Periodic maintenance, which consists ofwork items such as 'Regravelling' to

be carried out periodically every few years.

(iii) Special repairs, and flood and rain damage repairs, which consist of repairs

to the embankment, pavement, culverts, road furniture, etc. necessitated by

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landslides, earthquakes, cyclones, heavy rains/cloud bursts, floods etc; the

nature and extent of such repair works could not be foreseen or predicted.

(b) Before starting with the work, it should be ensured that adequate

arrangements (like erection of barriers, signs and red flags/light/reflectors) (Fig.

4.1) are made for the safety of traffic, workmen, pedestrians, cattle etc. The work

should be planned in such a way that inconvenience caused to the traffic is minimal.

Wherever possible, the work should be confined to half the pavement width at a

time, leaving the other halfto traffic.

4.1.4. Economic benefits ofmaintenance operations

Timely and proper maintenance of Gravel Roads can lead to significant economic

benefits. These include:

(i) Reduction in level of future maintenance and rehabilitation costs.

(ii) Improved safety and reduction in road closures.

(iii) Reduction in vehicle operating costs and accident costs.

4.2. Surface & Structural Defects on Gravel Roads

4.2.1. The defects observed on Gravel Roads are essentially the result of complex

interactions between the materials used, traffic type and volume, climatic conditions,

construction methods and quality control exercised. Broadly, the various defects can be

classified as:-

(a) Surface defects, observed in the upper layers of the pavement are due to

factors like poor compaction, unsatisfactory grading, climatic conditions,

poor quality of materials, inadequate drainage, neglect of routine and

preventive maintenance measures etc. or a combination of these. The surface

defects result in poor riding quality. The more common surface defects are:

- Corrugations

- Potholes

- Rutting

- Ravelling/Loose Material

- Surface Erosion/Dust Generation/Loss ofSurface Material

- Slippery Surface

- Soft Spots

(b) Structural Defects, are deep seated problems caused by overstressing of the

subgrade and/or the pavement. One ofthe common causes is lack ofdrainage, other

causes being substandard materials used and inadequate thickness of the pavement

for the design traffic. These defects are often characterized by shear failure in form

oflarge settlements and upheavals.

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MEN WORKING AHEADSIGNS

END OF WORKSITE SIGNS STOP/GO PADDLE

FOR TFIAFFICCONTROLLER

WORKER'S FLUORESCENT JACKET

TRUCK WITH REFLECTIVE MARKINGS

Fig. 4.1 : Some Safety Devices for the Workmen(Source:Intemational Road Maintenance Hand Book Vol. II, Maintenance

of Unpaved Roads, PIARC, Published by TRRL, UK)

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4.2.2. Surface defects can be removed by grading or planing the surface. However, gravel

roads with structural defects would require a more detailed investigation and treatment including

rehabilitation.

4.2.3. During the Condition Survey of any Gravel Road, it is necessary to make an

assessment of the severity of surface defects in terms of the severity being 'High', 'Mediun' or

'Low'. Such an assessment can be accomplished as under:

(a) Surface Roughness/Riding Quality (Refer para 2.5.2 Section 2)

An assessment shall be made in terms ofthe 'Pavement Condition Index' (PCI) on a rating

scale of5 to 1 as under:

Normal Safe Driving Speed (km/h)

Over 35

25-35

15-25

10-15

Less than 10

(b) Corrugations

PCI

5

4

3

2

1

A visual assessment of the corrugations shall be made by the bumps experienced while

travelling on the gravel road in ajeep or passenger car as under:

(i) Bumps can be felt and heard and significant

reduction in speed is required

(ii) Bumps can be felt and heard and some

reduction in speed is required

(iii) Bumps can be felt and heard but no

reduction in speed is required

High severity

Medium severity

Low severity

(c) Potholes

A visual assessment ofthe severity of'Potholing' shall be carried out as under:

(i) Depth ofpothole more than 50mm High severity

(ii) Depth ofpothole in the range 25 to 50mm Medium severity

(iii) Depth ofpothole less than 25 mm Low severity

(d) Rutting

The ruts or depressions ofthe surface in the wheel tracks shall be measured in mm and an

assessment ofthe severity level made as under:

(i) Depth ofrutting more than 50mm(ii) Depth ofrutting 25 to 50mm(iii) Depth ofrutting less than 25 mm

High severity

Medium severity

Low severity

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(e) Ravelling

An assessment of the percentage area of the ravelled surface shall be made and

severity level recorded as under:

(i) Percentage area ofravelled surface over 50 High severity

(ii) Percentage area ofravelled surface 25 to 50 Medium severity

(iii) Percentage area ofravelled surface < 25 Low severity

(f) Surface Erosion

Gravel roads are susceptible to longitudinal/transverse erosion by flow ofwater over the

road surface. An assessment of the severity level can be made by the bumpiness experienced

while driving in a car orjeep over the eroded surface, as under:

(i) Bumps can be felt and heard and significant

reduction in speed is required High severity

(ii) Bumps can be felt and heard and some

reduction in speed is required Medium severity

(iii) Bumps can be felt and heard but no

reduction in speed is required Low severity

(g) Dust Generation

An assessment of the dust nuisance shall be made by driving in a car/jeep at a speed

of 30-40 km/h and taking observations as under:

Dangerous loss of visibility - significant discomfort High severity

Some loss of visibility - no discomfort Medium severity

No loss of visibility Low severity

4.3. Maintenance of Gravel Roads

The maintenance methods commonly adopted for Gravel Roads are Grading, Dragging

Patching, RegraveUing and use ofDust Palliatives, described in sub-paras 4. 3.1 to 4.3.5.

4.3.1. Grading

4.3.1.1. It is a matter of vital importance that a good camber is always maintained on a

gravel road surface to enable the water to shed off readily. Such a maintenance effort can be

accomplished by regular 'Grading'. For Gravel Roads, the 'Grading' is also needed to restore

gravel from the shoulders which has been lost from the Gravel Road surface and the gravel thus

restored can be used to fill potholes and corrugations etc. Grading can be used to correct the

following defects:

- Loss of Shape

- Ruts

- Potholes

- Corrugations

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- Erosion Gullies

- Silted or Blocked Ditches

4.3.1.2. Grading is a 'Routine Maintenance' activity and can be carried out by tractor-

towed graders. The gravel road surface to be graded should first be prepared by patching of large

potholes or depressions and draining out areas of standing water etc. It may be necessary to

scarify the existing surface to cut to the bottom ofany surface defects and loosen the material for

reshaping. The process ofgrading can be carried out by tractor-towed grader (Fig. 4. 2). Grading

can be ofthree types, as under:

• Light Grading : When the gravel surface crust is not broken and it is a matter of

only spreading or raking back loose surface material to provide a "running course"

as protection ofthe surface crust.A light Grader or Drag can serve the purpose.

• Normal Grading : This is done when the surface crust is cut and it is necessary to

remove surface defects such as corrugations, ruts or potholes. In this case a 8-10

tonne Grader is suitable.

• Heavy Grading : This is required when the road is out of shape and in the process

of repair, and fairly heavy scarifying is required. This reshaping operation requires

a Grader in the 10-12 tonne mass range.

4.3.1.3. The Grader works on one side ofthe road at a time and works in passes about 200

metres long to convenient and safe turning points (Ref. 1 ). Light Grading will normally require 4

passes to reshape the road (Fig. 4.3). Heavy Grading will require additional passes to achieve the

required camber. Work should be completed on one side ofthe road at a time. An even number of

passes should be used to avoid a flat finished crown. The initial passes cut to the bottom of the

surface irregularity and deposit a windrow just beyond the centre line. If required, water should

be sprayed over the windrow. In order to avoid flattening the centre, the final pass should not be

made down the centre ofthe road with the grader blade horizontal (Fig. 4.4).

4.3.1.4. On sections where grading has been completed, the road roller should follow.

Normally about 8 passes of the roller are required to achieve full compaction, working towards

the centre. Shoulders should be treated as part ofthe running surface. Camber should be checked

with a Camber Board at about 1 00m intervals. On bends, the surface should be straight at 4 to 6 %from shoulder to shoulder. The shape ofthe road over the culverts should be maintained to avoid a

hump (Fig. 4.5). Where required, material should be brought from either side of the culvert to

maintain the required cover to the top ofthe culvert.

4.3.1.5. The number of times during the year each Gravel Road will need grading will

depend upon the amount of traffic using the road, climatic conditions in the area, local

topography and other physical features. In the absence of adequate experience in the area, the

Grading Frequency Chart developed by theTRRL ofUK (Fig. 4.6) may be used.

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LIGHT GRADiNG

200 m approx

HEAVY GRADING

Fig. 4.3 : Light and Heavy Grading

ource: International Road Maintenance Hand Book Vol. II,

Maintenance of Unpaved Roads, PIARC, Published

by the TRRL, UK)

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Fig. 4.4 : Avoid Flattening at tlie Centre (Ref 1)

(Source : International Road Maintenance Hand Book Vol. 11,

Maintenance ofUnpaved Roads, PIARC, Published by the TRRL, UK)

Fig. 4.5 : Avoid Hump at Culvert

(Source : International Road Maintenance Hand Book Vol. II, Maintenance of UnpavedRoads, PIARC, Published by the TRRL, UK)

8

50 100 150 200 250 300

Annual average daily traffic (vehicles per day)

Fig. 4.6: Grading Frequency Chart

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4.3.2. Dragging

4.3.2.1. Dragging is normally a Routine Maintenance task used to improve the gravel

road surface. Regular Dragging smoothens out minor defects in the road surface and removes

loose material from the surface. Where a running course of sand/gravel is used to cover the base

material for protection from traffic wear, frequent dragging is used to redistribute the running

course material disturbed by traffic plying over the surface.

4.3.2.2. Specially made drags towed by agricultural tractors can be used for Dragging.

Where the traffic plying on a rural road is of a low order, frequent dragging can reduce the need

for Grading. It is generally after a number of dragging operations that Grading is required.

Dragging will not remove corrugations once they are formed, nor will it restore camber or lost

material.

4.3.2.3. Dragging may be considered suitable only when development of road has been

carried out to a level when the pavement is structurally sound and where the loose running course

is less than 25 to 30mm in depth.

4.3.2.4. For various road conditions, the recommended plants are given below:

Road Condition Recommended Plant

Roads with depths of loose material in

excess of 20 mmBroom drag

Cutting drag using old grader blades.

Towed grader or light power grader.

Roads with roughness levels* less than

6000 mm/km with no appreciable loose

material

Timber framed drag or broom drag

Light grader or planer

Roads with roughness levels greater than

6000 mm/kmCutting drag using old grader blades.

Light grader, planer or mediumgrader

* Roughness measured using Bump Integrator

Drags should not be towed at speeds above 1 0 km/h and preferably should be towed at 5km/h. Abroom drag and roller can be seen in Fig. 4.7, while a typical tractor and timber drag are shown in

Fig. 4.8. In Fig. 4.9, it can be seen how a drag can be used to shift material from different parts of

the pavement.

4.3.2.5. It must be emphasised that Drags must be used at frequent enough intervals to

smoothen the road surface. Drags should not be used on roads which have deteriorated, due to

lack of frequent maintenance interventions, to a level where only heavy grading or reshaping is

the answer. Fig. 4.10 shows a multi-purpose tractor-towed equipment enabling an operator to

carry out a wide range ofmaintenance activities.

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Fig. 4.7 : A Broom Drag(Source:Unsealed Roads : A Manual of Repair and Maintenance

for Pavements, National Roads Board, New Zealand)

Fig 4.8 : Typical Tractor Towed Drag

(Source:Unsealed Roads : A Manual of Repair and Maintenance for

Pavements, National Roads Board, New Zealand)

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DRAG IN USE AS SEEN FROM ABOVE

DIRECTION OFTRAVEL

MATERIALBEING DRAWNFROM CENTREOF ROAD TO

SIDES

DIRECTION OFTRAVEL

MATERIALBEING DRAWNFROM SIDESTO CENTREOF ROAD

DIRECTION OF jT*>TRAVEL

MATERIALBEING

SMOOTHENED

Fig. 4.9 : Use of Drag in Drawing Material from Different Parts of Pavements

(SourceiUnsealed Roads : A Manual for Repair and Maintenance for

Pavements, National Roads Board, New Zealand)

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!

Fig. 4.10 : A Tractor-Towed Equipment Enabling the Operator to Carry out a

Variety of Maintenance Operations

(Source:Unsealed Roads : A Manual of Repair and Maintenance for

Pavements, National Roads Board, New Zealand)

4.3.3. Patching

4.3.3.1. Where potholes or depressions on the gravel road are large, patching is required

before grading. Sometimes, patching is required between grading or reshaping operations.

Patching can be used to repair eroded areas or can be used to restore areas which become soft

when wet. When the work involves material less than a truck or two, the repair work is termed

patching, while for large scale work, it is termed Spot Gravelling or Regravelling. Patching

cannot be used for repairing Corrugations but can be used to correct:

- Erosion Gullies

Where the potholes are large in numbers, scarifying will be needed with a grader and

possibly Regravelling.

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4.3.3.2. Gravel to be used for patching should be dumped by the road side where it is

required to be used. The quaHty of gravel should be at least as good as the gravel already used in

the road surfacing. The gravel should be dumped on the shoulder (Fig. 4.11) adjacent to the

location where the patching work is to be carried out. Care must be taken to see that the material

should not be dumped on the road surface.

4.3.3.3. In the pothole or rut, where patching work is to be carried out, any loose material

or standing water should be brushed out (Fig. 4.11). Where the potholes are large in size or are

very deep, the sides should be cut back to be vertical.

-V" (a) ' (b)

Fig. 4.11 :(a) Dump the material on the shoulder adjacent to location of patching work(b) Brush out any loose material or standing water

(Source: International Road Maintenance Hand Book Vol. II, Maintenance of UnpavedRoads, PIARC, Published by the TRRL, UK)

4.3.3.4. Check the moisture content of the material. If it is dry, the area to be patched

should be sprinkled with water and also water should be added to the material to be used for

patching. The area should be filled with gravel to a depth ofabout 100 mm. Ifthe material is dry,

it should be sprinkled with water to assist compaction.

4.3.3.5. The 1 00 mm layer at a water content close to OMC, should be compacted using a

roller or a hand rammer. In this manner, patching is built up in layers. The patched area is thus

filled up with gravel to about 30 mm proud of the surface level and is spread and raked to the

correct shape. The patch is compacted by a roller if the area is large and by hand rammer if the

area is small. Even for large areas, hand rammers will be required for the short edges and comers.

4.3.4. Regravelling

4.3.4.1. Regravelling is a periodic maintenance operation. Well before any significant

reduction in base thickness takes place and before the PCI rating reduces to the terminal PCI of

2.0, the task of 'Regravelling' must be accomplished. Regravelling can be carried out to correct

the following defects :-

- Loss ofshape

Ruts

- Potholes

- Erosion Gullies

Grading or Reshaping should be carried out before the regravelling operation.

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4.3.4.2. Gravel obtained from a quarry or gravel pit must meet the specified quality

requirements and the needed approval obtained before commencement ofthe work. The sections

where Regravelling is required should be marked at the site. The existing road surface must be

graded to provide a firm regular surface and the edges should be boxed to provide lateral support

for the fresh gravel. The graded surface should be watered to have the water content close to

OMC and roller compacted. The camber should be checked with a Camber Board and it should

fall within the specified range.

4.3.4.3. The Drainage System should be checked and repaired where necessary. The

excavated gravel should be stockpiled in low heaps to prevent segregation. After the initial

grading of the road is complete, the gravel should be transported to the regravelling site. The

dumping ofgravel should start at the far end ofthe site so that the gravel heaps do not come in the

way oftrucks delivering later loads.

Materials should be dumped at correct spacing on one side ofthe road only.

AWeekly Gravelling Plan should be prepared to indicate hauling distance etc.

4.3.4.4. Spreading ofthe gravel can start when there is a working length of at least 200 mof dumped material. Initially the road is sprayed with water. The Regravelling material is then

spread across the road using the grader. The material is then alternately spread by the grader and

watered until its moisture content is close to OMC. The material is then graded to produce the

specified camber. The camber should be checked with the Camber Board at approx. 100 mintervals along the road. If the desired camber is not achieved, the process of grading should be

repeated.

After the correct camber has been achieved, rolling can start, commencing at the edge

towards the centre. The roller should progress section to section at the same rate as the Grader.

About 8 passes are generally required to achieve full compaction.

4.3.5. Use ofdust palliatives

4.3.5.1. The main disadvantage being cited against gravel roads, is the dust generation,

considered as a safety hazard and pollutant to the environment. Besides being a safety hazard, a

very significant implication of dust generation is the loss of fines from the surface gravel which

leads to increased gravel loss and consequently more frequent maintenance. If, however, the

generation of dust can be controlled, the expenditure on gravel road maintenance can be

significantly reduced.

4.3.5.2. There is a wide variety of dust palliatives available which can be divided into 7

basic categories, as under:

(a) Water

(b) Water absorbing products (hygroscopic)

- Calcium Chloride brine and flakes

- Magnesium Chloride brine

- Sodium Chloride (Salt)

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(c) Organic Petroleum Products

- Asphalt emulsion

- CutbackAsphalt (LiquidAsphalt)

- Dust oils

- ModifiedAsphalt Emulsions

(d) Organic Nonpetroleum Products

- Animal Fats

- Lignosulphonate

- Molasses/Sugar Beet

- Tail Oil Emulsions

- Vegetable Oils

(e) Electrochemical Products

- Enzymes

- Ionic Products

- Sulphonated Oils

(f) Synthetic Polymer Products

- Polyvinyl Acetate

- Vinyl Acrylic

(g) ClayAdditives

- Bentonite

- Montmorillonite

4.3.5.3. The selection of type has to be based on the quantity of fines in the surface

material, climatic conditions and traffic volume. The following four categories of dust

palliatives appear suitable for Indian conditions:

(I) Water

(ii) Water absorbing products (hygroscopic)

(iii) Organic petroleum products

(iv) Clay additives

4.3.5.4. Prior to applying dust palliatives, all the surface defects should be removed,

gravel added to provide the correct shape/camber/superelevation and the surface compacted.

The surface should be dampened (except when non-emulsified petroleum products are used).

The dust palliative should then be applied uniformly over the surface. After light compaction.

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traffic may be allowed ifchlorides are used while for other products, some time may be required

for the product to get absorbed before allowing traffic. Field trial sections need to be laid and

their performance monitored to evaluate the efficacy ofa product.

4.4. Maintenance ofShoulders, Drainage and Structures

4.4.1. Inspection of drainage system, shoulders etc. in both dry and rainy seasons is

necessary for effective identification of various defects. In the dry season, structural damages

can be better identified and in the rainy season, actual functioning ofthe drainage system can be

evaluated. Any field supervisor must evaluate the extent of damage in order to quantify the

needed maintenance measures; such an evaluation can best be done by inspection on foot. The

supervisory staffshould look for:

(i) Ditch cross-section destroyed

(ii) Ponding in the ditch and shoulders

(iii) Silting

(iv) Uneven ditch invert, varying x-section

(v) Invert and sides ofditch eroded

(vi) Drain destroyed

(vii) Ditch lining damaged

(viii) Ponding/erosion

4.4.2. Given below are the common defects, their causes and measures needed for

rectification:

SL.

NO.DEFECTS CAUSES

MAINTENANCEMEASURES

1. Ditch cross

section

destroyed

Plying of

vehicles/movement of

animals

Reshaping/ Regrading of

ditch

2. Ponding in ditch

and on shoulder

Insufficient ditch x-

section

Deepening of ditch

3. Silting of drain Water flows slowly on the

invert slope

Desilting of ditch

4. Uneven ditch

invert

Blockage caused by

debris/vegetation

Clearing, cleaning and

regrading

5. Erosion of sides

and bottom of

ditch

Too steep gradient Reinforcing of ditch slopes,

regrading or realignment of

drain, ditch checks

6. Destruction of

lined or precast

drain

Poor alignment or change

in flow direction

Erosion control and

realignment of drain

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7. Ditch lining is

damagedSettlement/erosion of soil

under ditch

Erosion repair and lining

repair

8. Ponding, erosion In-sufficient lateral

drainage

Provision of lateral drainage

9. Silting, blockage

by aebns oi

culvert

Too flat gradient, in-

conect positioning of

culvert, floating debris

lodged in culvert

Clearing and cleaning and

provision oi debris rack.

1 AlU. Erosion of

stieam bed at

culvert outlet

Water flow veiy

fast/culvert invert on a flat

grade

™ * .

Erosion repair

11. Settlement

cracks on the

culvert

Settlement of soil below If minor cracks, only repair

01 cracks. In case oi major

settlement, the culvert must

be reconstructed.

12. Rusting of steel

in culvert

Weathering, poor quality

material

Repair of steel section

13. Cracks in paved

surface of

causeways

Settlement Sealing of cracks

14. Obstruction on

shoulders

Operational Removal of obstruction

15. Level of

shoulders higher

than carriageway

Transportation ofcarriageway material byraflfic, swelling of soils,

vegetation growth.

Regrading of shoulders

and surface vegetation

control.

16. Ruts, depressions

or Inadequate

Cross-slope in

shoulder

Erosion, plying of vehicles Patch work, reshaping and

camber correction

17. High vegetation

on shoulderUnchecked growth of

vegetation

Vegetation control

18. Level of shoulderlower thancarriageway

Erosion/settlement of

carriageway

Replenishment of shoulder

19. Vegetation

overgrowth on

slopes

Lack of grass cutting,

trimming

Vegetation control

20. Erosion of slopes

due to surface

water

Rain water accumulation at

the toD of the sloDes

Erosion repair by cut off

ditch, collector drains,

chutes, berms, vegetation

cover and masonryprotection

Source : Document on Rural Road Development in India Vol. II, CRRI, 1990

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4.4.3. Activities

(i) Reshaping/Regrading/Deepening of Ditches/Drains: These can be donemanually. Alignment should be set by string line and the materials within the

string line should be cut and removed. Cross section, grading and depth should

be checked and corrected. Wherever possible, motor grader can be used for

these activities. The excess material must be removed from site and in no case

should be spread on the road surface.

(ii) Clearing and cleaning of Ditches/Drains: Any object which can interfere

with water flow should be removed. These objects should be disposed of well

away from the road so that these cannot impede the water flow again.

(iii) Repair of Drain Erosion: This should be done by replacing and back filling the

lost soil. Permanent measures like masonry lining or precast drain can beconsidered.

(iv) Repair of Drain lining: Settled or damaged precast sections or loose stone

should be removed and underlying soil compacted. After addition of fresh

soils, the levels should be corrected and then only fresh stones or precast drain

should be laid.

(v) Vegetation control: Except in arid areas, once a year, grass and weed cutting

and bush clearance on the shoulders is a must. In case of earth or gravel roads

these activities may be required to be done more frequently. Tractor-towed mowercan be employed where available, but ordinary manual method should be sufficient

for the purpose. Dead or leaning trees should be removed from the roadside. Use ofchemicals or burning of the roadside vegetation should be avoided as these are

harmfiil.

4.5. Special Problems ofHill Road Maintenance

4.5.1. Some ofthe special problems ofhill road maintenance are:

(1) Snow clearance

(2) Slips and landslides

(3) Drainage

Snow Clearance

The roads in the Himalayan hill region get covered with snow. Snow clearance can be

done manually or by special equipment (dozers, snow masters and snow blasts).

Landslides and Slips

Landslides and slips are a common feature of hill roads. Road maintenance in

areas subjected to landslides and slips poses severe problems. The greatest of

them is quick removal of debris and restoration of traffic. Mechanical equipment

like dozers becomes very necessary.

Drainage maintenance

Maintenance of drainage structures is an important task in hill road

maintenance. The quick and efficient removal of water prevents slips and

landslides and road deterioration. Drainage arrangements such as catchwater

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drains, cross-drainage structures, side drains and subsurface drains should be

inspected before the monsoons and cleared ofall obstructions.

4.6. Maintenance Management

(a) General

The objectives of maintenance management are to plan and programme the

maintenance activities making optimal use of the resources of men, materials,

machinery and money so that the planned works are performed to a traffic-

worthy condition. The steps to achieve these objectives are discussed below.

(b) Road Data Banks

A proper management decision could be taken only when sufficient data are

available on the problem. Hence it is of vital necessity to collect and compile all

relevant data about the road and its environment and the resources available to

maintain the road network. These data should also be updated regularly. It is

reconmiended that the following data may be made available in the road data banks.

(i) Road cross-section including pavement composition (type and thickness),

shoulders, height ofembankment, side slope etc.

(ii) Geometries ofalignment

(iii) Details of various structures along the road viz., cross drainage structures,

roadside drains, breast walls, retaining walls, kilometre stones, traffic signs,

godowns etc.

(iv) Condition of the road-pavement surface condition (rutting, potholes etc.)

condition ofshoulder, and side drains.

(v) The maintenance history of the road - the date and type ofmaintenance put in

and its subsequent performance.

(vi) Traffic volumes and the quarterly rate and type ofaccidents.

Some of the road features are of a permanent nature like geometric design

features, cross-sectional details etc. and require to be updated only when there

is a major reconstruction. However, the road condition surveys (in terms of

PCI) and traffic counts etc. need to be updated at reasonable frequency. Each

State should possess a suitable machinery to collect, analyse and compile such

data which can be ofimmense use in maintenance management. A system of

road registers for each road can also be introduced.

(c) Standards of Maintenance

The next step in maintenance management will be to evolve reference standards

to help the maintenance staff to take the right decisions. In a systems concept,

there are three distinct types ofreference standards:

(i) Performance standards which define the level of quality below which the

various components ofthe road should not fall, so that the road users are given

a satisfactory level of service from the technical and economic points ofview.

These standards are the basis for determining when and what type of

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maintenance activities are to be provided to the road network. Rutting,

potholing etc. are the parameters used to assess the performance level;

(ii) Quantity standards, which indicate the resources required to achieve the

necessary level ofservice; and

(iii) Operational standards, which specify the working method and crew

requirement consistent with a reasonable level of productivity for each

maintenance activity possible. These standards can be revised and improved

based on the achieved possible output in the field.

(d) Operational Management

For proper management of the resources allocated for maintenance, the objectives

to be aimed at should be reduction in costs for a defined quality ofwork, better work

performance within the same cost and proper deployment ofmen and machinery to

ensure an optimal utilisation of the available resources. For this, it is necessary to

identify the basic maintenance activities, quantum of work needed in relation to

road performance standards and the resources needed to fulfil these tasks in terms

of materials, machinery and man-hours. Having done this, it would be easy to

prepare a work schedule for weekly, monthly, quarterly and yearly operations. In

this way, it will be possible to move from a purely financial accounting system to a

rational process ofanalytical management.

Modernisation of maintenance management may involve radical changes in

traditional working methods. Mobile system of gangs in the place of the

time-honoured labour groups, who are practically immobile and have little or

no equipment will go a long way in streamlining the routine maintenance work.

The maintenance personnel should also be given periodic training.

A simplified Rural Road Maintenance Management System is given below

(Fig. 4.12).

Road Inspection and Road

Inventory

Data E

Condition Rating

Base

Traffic Data

Maintenance Budget

Rating Scale

Prioritization of

Maintenance Intervention

r

Annual Maintenance

Programme

Fig. 4.12 : Flow Chart for Rural Road Maintenance Management System

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(e) Condition Rating in Terms ofPavement Condition Index (PCI)

The most simple rating scale for the Pavement Condition Index, is roughly, derived

from the speed oftravel, as under:

Normal Driving Speed (km/h) PCIOver 35 5

25 to 35 415 to 25 3

10 to 15 2

Less than 10 1

Akematively, the riding comfort observed when driving at a design speed of 40

km/h can be assessed as under:

Riding Comfort at 40 km/h PCISmooth and Pleasant Ride 5

Comfortable 4Slightly Uncomfortable 3

Rough and Bumpy 2Dangerous 1

(f) Prioritization ofMaintenance Interventions

The following prioritization scheme for maintenance intervention may be adopted.

SI.

No.

Condition of Road PCI Type of Intervention

1. Ridability is very poor and the

surface is very rough and uneven

< 1 Reconstruct immediately

2. Ridability is poor and the surface

is rough and uneven

1 to 2 Regravel Immediately;

routine maintenance to continue

3. Ridability is fair with intermittent

rough and uneven sections

2 to 3 Regravelling within 1 year;

routine maintenance to continue

4. Ridability is good with a few

slightly rough and uneven sections

3 to 4 Routine maintenance

5. Ridability is very good <4 Routine maintenance

4.7. Organizational!Aspects ofMaintenance Management

It is necessary to have a suitable organisational set-up for an effective implementation of

various maintenance measures. There should be a separate maintenance unit for rural roads in

each district, to carry out the monthly maintenance work programme. Depending on the nature of

the maintenance activities, the work could be outsourced to local people. The required

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implements/plant/equipment could be provided to the local contractors. Concerted efforts are

required to organise suitable training programmes for the staffofthe Maintenance Units and for

capacity building ofthe local contractors.

4.8. Do's and Don'ts

Do's Don'ts

1. Determine the cause of any surface defect before

taking any remedial action.

1. Do not undertake any maintenance

operations without Safety Measures at

2. During periodic maintenance and resurfacing work sites.

operations, restore the correct crossfall and 2. Do not attempt to compact fresh

sunerel evation giavci uy iiciiiic, wiiiiuui Using proper

3. Carefully select surface gravel to minimize dust compaction equipment.

nmn 1 ptti ^J. Do not overlook the maintenance of

4. Make all eiiorts to mamtam a good dramage system. me arainage system.

5. Scientifically decide upon the number of times

during the year that each unpaved road will need

grading, based on a range of factors.

4. Do not decrease or increase the

existing superelevation during

inainiendnce operdiions.

6. Retain superelevation on curves during maintenance

operations.

5. Do not disturb roadside vegetation

while carrying out various

7. Prefer simple maintenance equipment e.g, towedmaintenance tasks.

grader over a motor grader. 6. Do not decide upon the Dragging

8. Carry out a Condition Survey to determine PCI,frequency arbitrarily without practical

tests.atleast once a year, preferably twice, before and after

rainy season. 7. Do not ignore the maintenance of any

9. Adopt a systematic maintenance management system

as recommended in the Manual.

grass lining/ turfing provided to

control erosion.

10. Combine heavy grading with regravelling to restore

thickness of gravel surface.

8. Do not undertake any maintenance

task without considering the data

obtained during the last condition

survey.

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APPENDIX-A(Para 2.2.2.1 and 2.2.4)

PROPORTIONING DIFFERENT MATERIALS FOR ACHIEVING THEPRESCRIBED GRADING

A-1. Combining two materials

When only two materials are to be combined, a simple graphical methoddescribed below can be followed:

Steps:

It is required to blend sand (A) and silt-clay (B) to obtain the following gradation:

Sieve designation Percentage passing Material (A) Material (B)

4.75 mm 100 100

2.36 mm 80-100 91

1.18 mm 50-80 34 100

425 micron 30-60 10 84

300 micron 20-45 3 59

75 micron 10-25 2 36

(i) On a convenient size of rectangular graph, scale off top linearly from 100 to 0

as percentage of A in mix. Scale off the base corresponding from 0 to 100 as

percentage of B in mix. Scale off the vertical ordinate from 100 at top to 0 at

bottom on the left and 0 at top to 100 at bottom on the right, representing the

percentages passing sieve [Fig A-1].

(ii) On the left ordinate, mark off percentages passing the given sieves for material

A. On the right ordinate mark off percentages passing the given sieves for

material B.

(iii) For each sieve size, connect by a straight line the points, representing the

respective percentages passing each material. The intersection of each sieve line

by any vertical line will define the combined grading of the two materials mixed

in the proportions shown in the top and bottom horizontal scales.

(iv) On each sieve line, the specified percentage passing limits are marked by

small circles. The intercept lying between the circles represents, for any

particular sieve line, the range ofproportion that will comply the specification.

(v) If mixtures within the specification limits are possible, vertical lines can be

erected such that their intersection points with all sieve lines lie on the

acceptable intercepts. The highest and the lowest percentages of either material

at which this can be done represent the limiting mixtures which conform to the

specifications. The mid-point between the limiting mixtures will usually provide

the best mixture.

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100

80

>60

Oz.

COV)

I-

oLUOL

40

20

80

PERCENT OF MATERIAL A IN MIX

60 50 40 25 20

1

1

1

9 7« mi^ -—1

- -

I

1

8

1

y\1

1 r\

^^^^1

1

32 40 60 74 80

PERCENT OF MATERIAL B IN MIX

100

Fig. A- 1GRAPHICAL METHOD OF COMBINING TWO AGGREGATES

(vi) In the limits indicated are (i) 68 per cent A, 32 per cent B and (ii) 26

percent A, 74 per cent B. In practice, the acceptable properties would lie in the

range of A:B=2:1 to A:B=1:3. Probably aratio ofA:B=1:1 would be the best.

A-2. Combining Three Materials

In dealing with mechanical stabilisation, it is often found necessary to combine

different materials to obtain the finally desired gradation. Rothftach's graphical

method is a reasonably quick, accurate and simple method, and is used, for design

of cement concrete mixes, bituminous mixes and granular mixes. The method

consists ofthe following stages:

(i) Using the desired aggregate gradation, a distribution curve is plotted with the

percentage passing as linear ordinates and the sieve sizes on the horizontal scale. In

order to mark the sieve sizes on the horizontal scale, an inclined line (OA in

Fig. A-2) is first of all drawn. By marking the known percentages passing each size

sieve on this line and dropping vertically the intersection point to the horizontal

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axis, the location ofthe sieve size on the horizontal axis is determined.

(ii) The particle size distributions of the given materials to be blended are plotted on

this scale. The distribution curves will not generally be straight lines (Lines OB,CDE and CF GAin Fig. A-2).

mm mm mm mm mmSIEVE SIZE

Fig. A-2 : Rothfuch's Graphical Method of Combining 3 Materials

(iii) With the aid ofa transparent straight edge, straight lines are drawn representing the

particle size distribution in the best possible manner (Lines HJ and KA). This

means that the areas enclosed between the distribution curve and the straight line

should be minimum and are balanced about the line.

(iv) The opposite ends ofthese lines arejoined together (Lines BH and JK).

(v) The proportions for blending can be read offfrom the points where thejoining lines

cross the straight line representing the mixture. These points are L and M.

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The method is illustrated by the following example

:

Cols. 1 and 2 in the Table below give the gradation limits for various sieve sizes of a

stabilized soil mixture. Three materials are available, whose gradations are given in Cols. 4, 5

and 6. Work out the blending proportion.

Blending of Materials

Percentage passing

Sicv6 Required

Gradation

Materials Available

designation Average CoarseSand

Local 47% A

Limits Aggregates(B)

Soil 49% B

(A) (C) 4%C

(1) (2) (3) (4) (5) (6) (7)

40 mm 100 100 100 100

20 mm 80-100 90 75 88

10 mm 55-80 67.5 20 62

4.75 mm 40-60 50 8 100 53

2.36 mm 30-50 40 6 80 42

600 mm 15-30 22.5 2 40 21

75 micron 0-10 5 Nil 2 100 5

A reference to Fig. A-2 will illustrate the stages involved in the graphical method. The

percentages ofvarious materials as scaled out are:

Material (A) : 47%

Material (B) : 49%

Material (C) : 4%

The gradation of the final mixture on the basis of above blending indicated in Col. 7 of

the Table.

A-3 Combining two Soils for Producing the Mix Meeting Require Dplasticity

Index

Two Soils A and B with Plasticity indices P^ & Pg can be proportioned to produce a

material having the required plasticity index P. Record the values of P^ and Pg at the top

ends ofacross, P at the crossing point. Determine the numerical differences P^-P and P - Pg. The

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ratio in which the two soils should be mixed are indicated at the lower ends.

Mat . A : Mat . B :: P - Pg : - P

Example

:

The local soil-gravel in an area has a Plasticity Index (PI) of 30. Sand (PI = 0) is also

locally available from a nearby stream. What are the proportions in which the two can be

blended to obtain a PI of 1 0 in the mix?

Local Soil - Gravel p p

In the Mix, 1 0 parts ofLocal Soil - gravel (PI-30) need to be mixed with 20 parts ofSand (PI = 0)

from the nearby stream.

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BIBLIOGRAPHY

1 Road Statistical Abstract 1999.

2. AASHTO Guide for Design of Pavement Structures,AASHTO 1993.

3. Guide for Mechanistic-Empirical Design of New and Rehabilitated Pavement

structures-Final Report Part 4 Low Volume Roads, prepared for NCHRP,Transportation Research Board USA, March 2004.

4. The Massachusetts Unpaved RoadsBMP Manual, 2001

.

5. Unsealed Road Manual, Australian Road Research Board Ltd., May 1993.

6. Document on Rural Road Development in India Vol. I, CRRI 1990.

7. Gravel Roads : Maintenance and Design Manual, US Department of Transportation,

Federal Highway Administration (SDLTAP), Nov 2000.

8. Grameen Sampark (Ministry of Rural Development) Vol. I, No. 4, Oct-Dec. 2005.

9. Document on Rural Road Development in India, Vol. II, CRRI, 1990.

10. IS:1498: Classification and Identification of Soil for General Engineering Purpose.

1 1 . MORD Specifications for Rural Roads, Indian Roads Congress, 2004.

12. Road Gravels, Compendium 7, Transportation Research Board ofUSA.

13. Unsealed Roads : A Manual of Repair and Maintenance for Pavements, National

Roads Board, New Zealand, 1986.

14. Overseas Road Note No. 31, TRRL, U.K.

15. Sudhir Mathur, S.K. Soni, AVSR Murty 'Use of Low-cost Agricultural Implements in

Low Volume Road Construction, Transportation Research Record, USA.

16. MORT&H Manual for Construction and Supervision ofBituminous Works, IRC, 2001

.

17. International Road Maintenance Hand Book Vol. II, Maintenance of Unpaved Roads,

PIARC, published by the Transport Research Laboratory, U.K.

18. Road Maintenance and Regravelling (ROMAR) Using Labour-based Methods, Hand

Book, by C.A, Anderson, A Beusch and Derek Miles, Intermediate Technology

Applications, 1996.

19. Dust Palliative Selection and Application Guide, US. Dept. of Agriculture, Forest

Service Nov 1999.

20. Jones D, Sadzik E and Wolmarans, I 'The Incorporation of Dust Palliatives as a

Maintenance Option in Unsealed Road Management Systems, 20* Australian Road

Research Board Conference, March 2001.

84

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IRC:SP:77-2008

21. Kadiyali Dr. L.R, and Lai, Dr. N.B "Principles and Practices of Highway Engineering,

Khanna Publishers, Delhi, Fourth Edition, Third Reprint 2006.

22. IRCrSP: 20 Rural Roads Manual, 2002.

23. IRC:SP:26 Report Containing Recommendations of IRC Regional Workshops on Rural

Road Development, 1984.

24. IRC:SP: 42 Guidelines onRoad Drainage 1994.

25. IRC:SP:48 Hill Road Manual, 1998.

26. IRC:36 Recommended Practice for the Construction of Earth Embankments for Road

Works.

27. IRC:37 Guidelines for the Design of Flexible Pavements, 2001.

28. IRC:34 Recommendations for Road Construction in Water-logged Areas, 1970.

29. Quality Assurance Hand Book for Rural Roads, NRRDA, Ministry of Rural

Development 2007.

30. IRCiSP: 72 Guidelines for the Design of Flexible Pavements for Low Volume Rural

Roads, IndianRoads Congress, 2007.

31 . PMGSY Operations Manual, National Rural Road DevelopmentAgency, 2005.

32. Overseas Road Note 1, Maintenance Management for District Engineers, TRRL, UK,

1987.

33. Overseas Road Note 2, Maintenance Techniques for District Engineers, TRRL, UK,

1986.

85

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(The Official amendments to this document would be published by the IRCin its periodical, 'INDIAN HIGHWAYS', which shall be considered as

effective and as part of the code/guidelines/manual, etc. from the

date specified there in)